Magnetic tape container

ABSTRACT

The magnetic tape container includes a core around which a magnetic tape is wound. The magnetic tape includes a non-magnetic support, and a magnetic layer including a ferromagnetic powder. A maximum value of a deviation of a center position of an average minimum region reference circle of a trajectory of one rotation drawn by the magnetic tape, in a case where the wound magnetic tape is drawn out from the core core is 100 μm or less for three points of the magnetic tape in a width direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2021-030916 filed on Feb. 26, 2021. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape container.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for datastorage (for example, see JP6590102B).

SUMMARY OF THE INVENTION

Recording of data on a magnetic tape and reproducing of the recordeddata are usually performed while causing the magnetic tape to run in amagnetic recording and reproducing device (generally referred to as adrive) by repeating drawing the magnetic tape wound around one reel andwinding around the other reel between two reels. Data is recorded andthe recorded data is reproduced by a magnetic head in the drive withrespect to the magnetic tape running as described above.

It is generally said that the magnetic tape is excellent in terms ofcost performance compared to other recording media, because of its lowprice per data capacity to be recorded and low power consumption duringdata storage. The greater the data capacity to be recorded, the greaterthe cost advantage. Therefore, in recent years, the magnetic tape hasbeen attracting attention as a large-capacity data storage medium. In acase where a data transfer rate (writing speed and/or reading speed) isconstant, the greater the data capacity to be recorded, the longer thetime required to record the data and reproduce the recorded data. Thus,in order to further increase the capacity of the data to be recorded onthe magnetic tape, it is desirable to increase the data transfer rate(writing speed and/or reading speed) of the magnetic tape.

An object of an aspect of the invention is to make it possible toimprove a transfer rate during recording of data on a magnetic tapeand/or reproducing of the data recorded on magnetic tape.

According to an aspect of the invention, there is provided a magnetictape container comprising:

a core around which a magnetic tape is wound,

in which the magnetic tape includes a non-magnetic support, and amagnetic layer including a ferromagnetic powder, and

a maximum value of a deviation of a center position of an averageminimum region reference circle of a trajectory of one rotation drawn bythe magnetic tape, in a case where the wound magnetic tape is drawn outfrom the core core(hereinafter, also referred to as a “reference circlecenter position deviation”) is 100 μm or less for three points of themagnetic tape in a width direction.

In one embodiment, the magnetic tape may have a servo pattern on themagnetic layer.

In one embodiment, an entire length of the magnetic tape may be 200 m ormore.

In one embodiment, the maximum value of the deviation of the centerposition of the average minimum region reference circle may be 80 μm orless for the three points.

In one embodiment, the maximum value of the deviation of the centerposition of the average minimum region reference circle may be 55 μm orless for the three points.

In one embodiment, the magnetic tape may further include a non-magneticlayer including a non-magnetic powder between the non-magnetic supportand the magnetic layer.

In one embodiment, the magnetic tape may include a back coating layerfurther containing a non-magnetic powder on a surface side of thenon-magnetic support opposite to a surface side provided with themagnetic layer.

In one embodiment, the magnetic tape container may be a magnetic tapecartridge.

In one embodiment, the magnetic tape container may be a magneticrecording and reproducing device and may further include a magnetichead.

In one embodiment, the magnetic head may include a reproducing elementhaving a reproducing element width of 0.8 μm or less.

In one embodiment, the magnetic recording and reproducing device mayfurther include a tension adjusting mechanism which adjusts a tensionapplied in a longitudinal direction of the magnetic tape which runs inthe magnetic recording and reproducing device.

In one embodiment, a vertical squareness ratio of the magnetic tape maybe 0.60 or more.

According to one aspect of the invention, it is possible to improve thetransfer rate during recording of data on a magnetic tape and/orreproducing of the data recorded on magnetic tape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a magnetic tape cartridge.

FIG. 2 is a perspective view in a case where a magnetic tape is startedto be wound around a reel.

FIG. 3 is a perspective view in a case where the magnetic tape has beenwound around the reel.

FIG. 4 shows a schematic view of an example of a magnetic recording andreproducing device in a state in which a magnetic tape cartridge isinserted.

FIG. 5 shows a schematic view of an example of the magnetic recordingand reproducing device.

FIG. 6 shows a schematic view of a state in which a magnetic tapecartridge having an opening portion formed in a case is mounted on themagnetic recording and reproducing device shown in FIG. 4.

FIG. 7 is an explanatory diagram of a curvature of a magnetic tape in alongitudinal direction.

FIG. 8 shows an example of disposition of data bands and servo bands.

FIG. 9 shows a servo pattern disposition example of a linear-tape-open(LTO) Ultrium format tape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the invention relates to a magnetic tape containerincluding a core around which a magnetic tape is wound. The magnetictape includes a non-magnetic support, and a magnetic layer including aferromagnetic powder. A maximum value of a deviation of a centerposition of an average minimum region reference circle of a trajectoryof one rotation drawn by the magnetic tape, in a case of drawing thewound magnetic tape out from the core (reference circle center positiondeviation) is 100 μm or less for three points of the magnetic tape in awidth direction.

In a magnetic recording and reproducing device which uses a magnetictape as a magnetic recording medium, a magnetic head is usually embeddedin the magnetic recording and reproducing device, whereas the magnetictape is treated as a removable medium (so-called replaceable medium).For example, a magnetic tape cartridge containing the magnetic tape isinserted into the magnetic recording device, and the magnetic tape iscaused to run between a reel of the magnetic tape cartridge and awinding reel embedded in the magnetic recording and reproducing deviceto record data on the magnetic tape and/or reproduce the data recordedon the magnetic tape. After that, the magnetic tape is accommodated inthe magnetic tape cartridge and the magnetic tape cartridge is extractedfrom the magnetic recording and reproducing device. In such an aspect,the magnetic tape cartridge can be the magnetic tape container, and thecore can be a reel provided in the magnetic tape cartridge.

In another aspect, the magnetic tape is not treated as the replaceablemedium, and the magnetic tape is accommodated in a magnetic recordingand reproducing device including a magnetic head. In such an aspect, themagnetic recording and reproducing device can be the magnetic tapecontainer, and the core can be a reel provided in the magnetic recordingand reproducing device.

The configuration of the magnetic tape cartridge and the magneticrecording and reproducing device will be further described later.

As described above, recording of data on a magnetic tape and reproducingof the recorded data are usually performed while causing the magnetictape to run in a magnetic recording and reproducing device by repeatingdrawing the magnetic tape wound around one reel and winding around theother reel between two reels. Specifically, the recording of data on amagnetic tape is normally performed by causing the magnetic tape to runin the magnetic recording and reproducing device and causing a magnetichead to follow a data band of the magnetic tape to record data on thedata band. Accordingly, a data track is formed on the data band. Inaddition, in a case of reproducing the recorded data, the magneticrecording and reproducing device is caused to run in the magnetic tapeand the magnetic head is caused to follow the data band of the magnetictape, thereby reading data recorded on the data band. In order toincrease an accuracy with which the magnetic head follows the data bandof the magnetic tape in the recording and/or the reproducing, a systemthat performs head tracking using a servo signal (hereinafter, referredto as a “servo system”) is practiced. In addition, the dimensioninformation of the magnetic tape in the width direction during therunning can be obtained using a servo signal, and the dimension of themagnetic tape in the width direction can be controlled by adjusting thetension applied in the longitudinal direction of the magnetic tapeaccording to the obtained dimension information (as an example, seeparagraph 0171 and the like of JP6590102B). It is considered that thetension adjustment can contribute to suppressing the magnetic head forrecording and reproducing the data from being deviated from a trackposition of a target track due to a width deformation of the magnetictape during the recording and reproducing to cause occurrence ofphenomena such as overwriting of the recorded data, reproducing failure,and the like.

In regard to the position deviation of the magnetic tape in the widthdirection, the present inventors conducted studies to improve thetransfer rate of the magnetic tape during the recording of the data onthe magnetic tape and/or the reproducing of the data recorded on themagnetic tape (hereinafter, simply referred to as a “transfer rate”),and surmised that the occurrence of position deviation of the magnetictape in the width direction in a period shorter than a period in whichthe tension adjustment is performed, in a case of drawing out the woundmagnetic tape, can be a reason of a decrease of the transfer rate.Specifically, the present invention surmised that, regardless of whetheror not the above tension adjustment is performed, the position deviationof the magnetic tape in the width direction in such a short period canbe a reason for increasing a frequency of performing “start/stop” or“repositioning” in which the magnetic recording and reproducing devicetemporarily stops the running of the magnetic tape and the magnetic tapeis reversed to write or read out data again. The more frequently“start/stop” and/or “repositioning” is performed, the longer it takes towrite and/or read out the data, resulting in a decrease of the transferrate. As a result of further intensive studies, the present inventorsnewly found that, as an indicator related to the position deviation inthe width direction in the short period, the reference circle centerposition deviation of the trajectory during drawing out the magnetictape which will be described in detail later is used, and by settingeach of these values to be in the range described above, it is possibleto improve the transfer rate during the recording of the data on themagnetic tape and/or reproducing of the recorded data. However, theinvention is not limited to other surmises described in thisspecification including the above surmise.

Hereinafter, the magnetic tape container will be described morespecifically.

Aspect of Magnetic Tape Container (Magnetic Tape Cartridge)

An aspect of the magnetic tape container is a magnetic tape cartridge.

The magnetic tape cartridge (hereinafter, also simply referred to as“cartridge”) is accommodated in a cartridge main body in a state wherethe magnetic tape is wound around a reel (core). The core around whichthe magnetic tape is wound in the magnetic tape container such as thereel of the cartridge is composed of at least a hub, and usually,flanges are provided at both end portions of the hub. The core of themagnetic tape container is rotatably provided inside the magnetic tapecontainer. As the magnetic tape cartridge, a single reel type magnetictape cartridge including one reel in a cartridge main body and a twinreel type magnetic tape cartridge including two reels in a cartridgemain body are widely used. In a case where the single reel type magnetictape cartridge is mounted in the magnetic recording and reproducingdevice in order to record and/or reproduce data on the magnetic tape,the magnetic tape is drawn from the magnetic tape cartridge and woundaround the reel (hereinafter, also referred to as a “winding reel”)provided in the magnetic recording and reproducing device. A magnetichead is disposed on a magnetic tape transportation path from themagnetic tape cartridge to a winding reel. Drawing out and winding ofthe magnetic tape are performed between a reel (supply reel) of themagnetic tape cartridge and a reel (winding reel) of the magneticrecording and reproducing device. In the meantime, for example, themagnetic head comes into contact with and slides on the surface of themagnetic layer of the magnetic tape, and accordingly, the recordingand/or reproducing of data is performed. With respect to this, in thetwin reel type magnetic tape cartridge, both reels of the supply reeland the winding reel are provided in the magnetic tape cartridge. Themagnetic tape container can be a single reel type magnetic tapecartridge in one embodiment, and can be a twin reel type magnetic tapecartridge in another embodiment. In a case where the magnetic tapecontainer is a twin reel type magnetic tape cartridge, the core fromwhich the magnetic tape is drawn out for the measurement of thereference circle center position deviation, which will be described indetail later, is a reel around which more parts of the magnetic tape arewound, in a state where the magnetic tape cartridge is not used, amongthe two reels. Regarding the single reel type and twin reel typemagnetic tape cartridges, the reference circle center position deviationmeasurement which will be described in detail later is performed usingan unused magnetic tape cartridge. In the present invention and thepresent specification, the term “unused” with respect to the magnetictape container (for example, the magnetic tape cartridge or the magneticrecording and reproducing device) means that the running of the magnetictape accommodated in the magnetic tape container is not performed afterbeing provided as a product. In one embodiment, the magnetic tapecontainer is preferably a single reel type magnetic tape cartridge thathas been mainly adopted in recent years in the field of data storage.

The hub of the core is a cylindrical member that configures an axialcenter portion around which the magnetic tape is wound. The hub of thecore can be a single-layer cylindrical member or can be a multi-layeredcylindrical member having two or more layers. From viewpoints ofmanufacturing cost and ease of manufacturing, the hub of the core ispreferably a single-layer cylindrical member. Examples of the materialconstituting the hub of the core such as the reel of the magnetic tapecartridge include a resin and a metal.

A thickness of the hub is preferably in a range of 2.0 to 3.0 mm, fromviewpoints of satisfying both a strength of the hub and a dimensionalaccuracy during molding. The thickness of the hub means a totalthickness of such multiple layers for a hub having a multi-layerstructure of two or more layers. An outer diameter of the hub is usuallydetermined by the standard of the magnetic recording and reproducingdevice, and can be in a range of, for example, 20 to 60 mm.

Hereinafter, the configuration of the magnetic tape cartridge will bedescribed with reference to the drawings. However, the aspect shown inthe drawings is an example, and the present invention is not limited tosuch an example.

FIG. 1 is a perspective view of an example of a magnetic tape cartridge.FIG. 1 shows a single reel type magnetic tape cartridge.

A magnetic tape cartridge 10 shown in FIG. 1 includes a case 12. Thecase 12 is formed in a rectangular box shape. The case 12 is generallymade of a resin such as polycarbonate. Inside the case 12, only one reel20 is rotatably accommodated.

FIG. 2 is a perspective view in a case where a magnetic tape is startedto be wound around a reel. FIG. 3 is a perspective view in a case wherethe magnetic tape has been wound around the reel.

The reel 20 includes a cylindrical reel hub 22 that constitutes an axialcenter portion. The reel hub is as described above in detail.

Flanges (lower flange 24 and upper flange 26) protruding outward in aradial direction from an upper end portion and a lower end portion ofthe reel hub 22, respectively are provided on both end portions of thereel hub 22. Here, regarding “upper” and “lower”, in a case where themagnetic tape cartridge is mounted on the magnetic recording andreproducing device, a side located above is referred to as “upper” and aside located below is referred to as “lower”. One or both of the lowerflange 24 and the upper flange 26 is preferably configured integrallywith the reel hub 22, from a viewpoint of reinforcing the upper endportion side and/or the lower end portion side of the reel hub 22. Theterm “integrally configured” means that it is configured as one member,not as a separate member. In a first embodiment, the reel hub 22 and theupper flange 26 are configured as one member, and this member is joinedto the lower flange 24 configured as a separate member by a well-knownmethod. In a second embodiment, the reel hub 22 and the lower flange 24are configured as one member, and this member is joined to the upperflange 26 configured as a separate member by a well-known method. Thereel of the magnetic tape cartridge may be in any form. Each member canbe manufactured by a well-known molding method such as injectionmolding.

A magnetic tape T is wound around an outer circumference of the reel hub22 starting from a tape inner terminal Tf (see FIG. 2). A tensionapplied in the longitudinal direction of the magnetic tape in a case ofwinding the magnetic tape around the reel hub is preferably 1.5 N(Newton) or less, more preferably 1.0 N or less, and also preferablytension-free.

A side wall of the case 12 has an opening 14 for drawing out themagnetic tape T wound around the reel 20, and a leader pin 16 that isdrawn out while being locked by a drawing member (not shown) of themagnetic recording and reproducing device (not shown) is fixed to a tapeouter terminal Te drawn out from this opening 14.

In addition, the opening 14 is opened and closed by a door 18. The door18 is formed in a shape of a rectangular plate having a size capable ofclosing the opening 14, and is biased by a bias member (not shown) in adirection of closing the opening 14. In a case where the magnetic tapecartridge 10 is mounted on the magnetic recording and reproducingdevice, the door 18 is opened against a bias force of the bias member.

A well-known technology relating to the magnetic tape cartridge can beapplied for other details of the magnetic tape cartridge.

In the above aspect, the magnetic tape is treated as a removable medium(so-called replaceable medium), and a magnetic tape cartridge (magnetictape container) accommodating the magnetic tape can be inserted into themagnetic recording and reproducing device, and the magnetic tapecartridge accommodating the magnetic tape can also be extracted from themagnetic recording and reproducing device.

FIG. 4 shows a schematic view of an example of a magnetic recording andreproducing device in a state in which a magnetic tape cartridge isinserted. In FIG. 4, the magnetic tape cartridge 10 is inserted into ahousing H of a magnetic recording and reproducing device 60, themagnetic tape T is drawn out into the housing H and is wound around awinding reel 606. The housing H can be formed of metal, a resin, or thelike.

Regarding the magnetic tape cartridge 10, the above descriptionregarding the single reel type magnetic tape cartridge can be referredto.

The recording and reproducing of data on the magnetic tape T areperformed by controlling a recording and reproducing head unit 602 inaccordance with a command from a control device 601.

The magnetic recording and reproducing device 60 has a configuration ofdetecting and adjusting a tension applied in a longitudinal direction ofthe magnetic tape from spindle motors 607A and 607B and driving devices608A and 608B which rotatably control a cartridge reel 20 and a windingreel 606.

The magnetic recording and reproducing device 60 has a configuration inwhich the magnetic tape cartridge 10 can be mounted.

The magnetic recording and reproducing device 60 includes a cartridgememory read and write device 604 capable of performing reading andwriting with respect to the cartridge memory 27 in the magnetic tapecartridge 10. The cartridge memory can be, for example, a non-volatilememory, and, in one aspect, the information related to the tensionadjustment which will be described later is recorded in advance or theinformation related to the tension adjustment is recorded. Theinformation related to the tension adjustment is information foradjusting the tension applied in the longitudinal direction of themagnetic tape.

A terminal or a leader pin of the magnetic tape T is drawn out from themagnetic tape cartridge 10 inserted into the housing H of the magneticrecording and reproducing device 60 by an automatic loading mechanism ormanually and passes on a recording and reproducing head through guiderollers 605A and 605B so that a surface of a magnetic layer of themagnetic tape T comes into contact with a surface of the recording andreproducing head of the recording and reproducing head unit 602, andaccordingly, the magnetic tape T is wound around the winding reel 606.In one embodiment, the magnetic head comes into contact with and slideson the surface of the magnetic layer of the magnetic tape, in a case ofrecording data on the magnetic tape and/or reproducing the data recordedon the magnetic tape in the magnetic recording and reproducing device.Such a magnetic recording and reproducing device is generally called asliding type drive or a contact sliding type drive. In another aspect,in the magnetic recording and reproducing device, the magnetic headperforms the recording of the data on the magnetic tape and/or thereproducing of the data recorded on the magnetic tape in a contactlessstate with the surface of the magnetic layer, except for a case ofrandom contact. The magnetic recording and reproducing device of theaspect is generally called a floating type drive.

The rotation and torque of the spindle motor 607A and the spindle motor607B are controlled by a signal from the control device 601, and themagnetic tape T runs at random speed and tension. A servo patternpreviously formed on the magnetic tape can be used to control the tapespeed. A tension detection mechanism may be provided between themagnetic tape cartridge 10 and the winding reel 606 to detect thetension. The tension may be adjusted by using the guide rollers 605A and605B in addition to the control by the spindle motors 607A and 607B.

The cartridge memory read and write device 604 is configured to be ableto read and write information of the cartridge memory 27 according tocommands from the control device 601. As a communication system betweenthe cartridge memory read and write device 604 and the cartridge memory27, for example, an international organization for standardization (ISO)14443 system can be used.

The control device 601 includes, for example, a controller, a storageunit, a communication unit, and the like.

The recording and reproducing head unit 602 is composed of, for example,a recording and reproducing head, a servo tracking actuator foradjusting a position of the recording and reproducing head in a trackwidth direction, a recording and reproducing amplifier 609, a connectorcable for connecting to the control device 601. The recording andreproducing head is composed of, for example, a recording element forrecording data on a magnetic tape, a reproducing element for reproducingdata of the magnetic tape, and a servo signal reading element forreading a servo signal recorded on the magnetic tape. For example, oneor more of each of the recording elements, the reproducing element, andthe servo signal reading element are mounted in one magnetic head.Alternatively, each element may be separately provided in a plurality ofmagnetic heads according to a running direction of the magnetic tape.

The recording and reproducing head unit 602 is configured to be able torecord data on the magnetic tape T according to a command from thecontrol device 601. In addition, the data recorded on the magnetic tapeT can be reproduced according to a command from the control device 601.

The control device 601 has a mechanism of controlling the servo trackingactuator so as to obtain a running position of the magnetic tape from aservo signal read from a servo band during the running of the magnetictape T and position the recording element and/or the reproducing elementat a target running position (track position). The control of the trackposition is performed by feedback control, for example. The controldevice 601 has a mechanism of obtaining a servo band interval from servosignals read from two adjacent servo bands during the running of themagnetic tape T. The control device has a mechanism of adjusting andchanging the tension applied in the longitudinal direction of themagnetic tape by controlling the torque of the spindle motor 607A andthe spindle motor 607B and/or the guide rollers 605A and 605B so thatthe servo band interval becomes a target value. The adjustment of thetension is performed by feedback control, for example. In addition, thecontrol device 601 can store the obtained information of the servo bandinterval in the storage unit inside the control device 601 disposed inthe housing H of the magnetic recording and reproducing device 60, astorage device (not shown) disposed in the housing H as a devicedifferent from the control device, a cartridge memory 27, an externalstorage device (not shown) disposed outside of the housing H, and thelike.

In the magnetic recording and reproducing device 60, the tension can beapplied in the longitudinal direction of the magnetic tape during therecording and/or reproducing. The tension applied in the longitudinaldirection of the magnetic tape is a constant value in one embodiment andchanges in another embodiment. For example, as described above, atension detection mechanism can be provided for detection between themagnetic tape cartridge 10 and the winding reel 606 in FIG. 4. Inaddition, for example, the tension can also be controlled by the controldevice or the like of the magnetic recording and reproducing devicedevice so that a minimum tension is not less than a value determined bya standard or a recommended value and/or a maximum tension is notgreater than a value determined by a standard or a recommended value.For example, in this way, by the tension adjusting mechanism capable ofadjusting the tension applied to the longitudinal direction of themagnetic tape which runs in the magnetic recording and reproducingdevice, it is possible to variably control the tension applied to thelongitudinal direction of the magnetic tape. Preferably, the dimensionof the magnetic tape in the width direction can be controlled byadjusting the tension applied in the longitudinal direction of themagnetic tape. In the tension adjustment, the tension applied in thelongitudinal direction of the magnetic tape can be changed.

The recording of the data on the magnetic tape is performed whilecausing the magnetic tape T to run between the winding reel 606 and thecartridge reel 20. The reproducing of the data recorded on the magnetictape is also performed while causing the magnetic tape T to run betweenthe winding reel 606 and the cartridge reel 20. After the recordingand/or reproducing ends, the magnetic tape T is usually wound around thecartridge reel 20 of the magnetic tape cartridge 10, and the entirelength of the magnetic tape T is accommodated in the magnetic tapecartridge 10. The magnetic tape cartridge 10 accommodating the magnetictape T is held in the housing H of the magnetic recording andreproducing device 60 in one aspect, and is extracted from the housing Hin the other aspect. A thermo-hygrometer 610 can be arbitrarily disposedin the housing H of the magnetic recording and reproducing device 60.The temperature and humidity inside the housing H of the magneticrecording and reproducing device 60 can be measured and monitored by thethermo-hygrometer 610.

Other Aspect of Magnetic Tape Container (Magnetic Recording andReproducing Device)

The other aspect of the magnetic tape container is the magneticrecording and reproducing device. In this aspect, the magnetic tape isnot treated as a replaceable medium, and the magnetic tape and themagnetic head are accommodated in the magnetic tape container (magneticrecording and reproducing device). In the present embodiment, the corefrom which the magnetic tape is drawn out for the measurement ofreference circle center position deviation, which will be described indetail later, is a reel around which more parts of the magnetic tape arewound in a state where the magnetic recording and reproducing device isnot used, among the two reels in the magnetic recording and reproducingdevice. In addition, in the present embodiment, the measurement ofreference circle center position deviation, which will be described indetail later, is performed using the magnetic recording and reproducingdevice in an unused state.

FIG. 5 shows a schematic view of an example in which a reel on which amagnetic tape is wound and a magnetic recording and reproducing deviceare integrated as an example of the embodiment. In FIG. 5, a tape reel911A and a tape reel 911B are fixed in the housing H of a magneticrecording and reproducing device 90, and the magnetic tape T is nottreated as a replaceable medium. The recording of the data on themagnetic tape is performed while causing the magnetic tape T to runbetween the tape reels 911A and 911B. The reproducing of the datarecorded on the magnetic tape is also performed while causing themagnetic tape T to run between the tape reels 911A and 911B. After theend of recording and/or reproducing, the magnetic tape T is usuallystored in the magnetic recording and reproducing device 90 with most ofit wound around the tape reel 911A or the tape reel 911B.

For the housing H, a control device 901, a recording and reproducinghead unit 902, guide rollers 905A and 905B, spindle motors 907A and907B, driving devices 908A and 908B, a recording and reproducingamplifier 909, and a thermo-hygrometer 910 in FIG. 5, the abovedescription for each part of FIG. 4 can be referred to. For the tapereels 911A and 911B, the above description for each part of FIGS. 2, 3,and 4, respectively, can be referred to.

The magnetic recording and reproducing device 90 includes a storagedevice 912 accommodated in the housing H and an external storage device913 disposed outside the housing H. The control device 901 can store,for example, information on the servo band interval obtained asdescribed above with respect to FIG. 4 in the storage device 912 and/orthe external storage device 913.

In any aspect, the entire length of the magnetic tape accommodated inthe magnetic tape container is not particularly limited, and can be, forexample, 200 m or more, or 800 m or more (for example, in a range ofapproximately 800 m to 2500 m). The longer the entire length of the tapeaccommodated in one magnetic tape container is, the more preferable itis from a viewpoint of increasing the capacity of the magnetic tapecontainer.

Magnetic Tape Reference Circle Center Position Deviation

For the magnetic tape accommodated in the magnetic tape container, amaximum value of a deviation of a center position of an average minimumregion reference circle of a trajectory of one rotation drawn by themagnetic tape, in a case of drawing the wound magnetic tape out from thecore (reference circle center position deviation) is 100 μm or less forthree points of the magnetic tape in a width direction. The presentinventors adopted the reference circle center position deviation as anindicator of the position deviation in the width direction in the shortperiod described above. The inventors consider that the fact that thereference circle center position deviation is 100 μm or less means thatthe magnetic tape is a magnetic tape in which the position deviation inthe width direction in the short period described above is suppressed,and this makes it possible to improve the transfer rate. In addition,from a viewpoint of further improving transfer rate, the referencecircle center position deviation is preferably 95 μm or less, morepreferably 90 μm or less, even more preferably 85 μm or less, stillpreferably 80 μm or less, still more preferably 75 or less, still evenmore preferably 70 μm or less, still further preferably 65 μm or less,still further more preferably 60 μm or less, still further even morepreferably 55 μm or less, and particularly preferably 50 μm or less.Further, the reference circle center position deviation can be, forexample, 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more.It is preferable that this value is smaller, from a viewpoint of furtherimproving the transfer rate. The method for controlling the referencecircle center position deviation will be described later.

The “reference circle center position deviation” in the presentinvention and the present specification is a value obtained by thefollowing method.

The following measurements are performed in a measurement environmentwhere an atmosphere temperature is in a range of 20° C. to 25° C. and arelative humidity is in a range of 40% to 60%. In order to acclimatizethe device used for the measurement and the magnetic tape container tobe measured to the measurement environment, the measurement is performedafter placing them in the measurement environment for at least one day.

Hereinafter, the measurement method will be described by taking the casewhere the magnetic tape container to be measured is a single reel typemagnetic tape cartridge as an example.

In order to draw out the magnetic tape from the reel (core) of themagnetic tape cartridge, a magnetic recording and reproducing device(drive) in which the magnetic tape cartridge can be attached anddetached is used. In order to observe a surface of the magnetic tapedrawn out from the reel (core) and an upper surface of the upper flangeof the reel in the case of the magnetic tape cartridge while being setin the drive, the following processing is performed on the magnetic tapecartridge.

After the magnetic tape cartridge to be measured is placed in themeasurement environment for one day or longer, the reel around which themagnetic tape is wound is extracted from the case of the magnetic tapecartridge. The reel is extracted in the measurement environmentdescribed above. In a case where a leader tape and/or a leader pin isattached to the magnetic tape wound around the reel, the extractiondescribed above is performed in a state where these are attached. Thereel extracted as described above (the magnetic tape is wound) is placedin the measurement environment until it is transferred to a case havingan opening portion. In a case where the magnetic tape cartridge containsa cartridge memory, the cartridge memory is extracted as well. Theextracted reel and cartridge memory are transferred to the case of thecartridge provided with the opening portion, so that the upper surfaceof the upper flange on the reel and the surface of the magnetic tape canbe observed with an optical discrimination sensor and a laserdisplacement meter, respectively, from the exterior of the case. Thetransfer to the case provided with the opening portion is carried out inthe above measurement environment. Alternatively, the case of themagnetic tape cartridge to be measured may be processed to form theopening portion described above. The processing for forming the openingportion is carried out while the reel around which the magnetic tape iswound is accommodated in the case, or after the reel around which themagnetic tape is wound is once extracted from the case. The reel isextracted in the measurement environment after the magnetic tapecartridge to be measured is placed in the measurement environment forone day or longer. In a case where a leader tape and/or a leader pin isattached to the magnetic tape wound around the reel, the extractiondescribed above is performed in a state where these are attached. Thereel extracted as described above (the magnetic tape is wound) is placedin the measurement environment until it is accommodated again in thecase after molding the opening portion. In a case where the processingfor forming the opening portion is performed while the reel around whichthe magnetic tape is wound is accommodated in the case, the magnetictape cartridge to be measured is placed in the above measurementenvironment for one day or longer, and then the opening portion isformed in the measurement environment. The opening portion can be formedby a well-known method.

A seal or the like that reflects light is attached to the upper surfaceof the upper flange of the reel, and the rotation period of the reel(core) of the magnetic tape cartridge is detected by detecting this withan optical discrimination sensor or the like during measurement. As theoptical discrimination sensor, for example, an optical discriminationsensor capable of emitting light having a spot diameter of about 5 mmand capable of externally outputting an electric signal synchronizedwith the index can be used. Specific examples include CZ-H35S andCZ-C21A manufactured by KEYENCE.

As a laser displacement meter for measuring the displacement of thesurface of the magnetic tape drawn from the reel (core), a laserdisplacement meter having a laser spot diameter of 1.5 mm or less, adisplacement resolution of 0.5 μm or less, and a time resolution of 50μsecond or shorter, and capable of externally outputting an electricsignal according to the displacement amount is used. Specific examplesof the laser displacement meter that can be used include LK-G85 andLK-GD500 manufactured by KEYENCE.

The magnetic tape cartridge is inserted into the magnetic recording andreproducing device and the magnetic tape is loaded. The magneticrecording and reproducing device used for the measurement may be of anystandard and generation as long as the magnetic tape cartridge can bemounted and the magnetic tape accommodated in the magnetic tapecartridge can run. In a case where the reel of the magnetic tapecartridge to be measured (the magnetic tape is wound) and the cartridgememory are transferred to another magnetic tape cartridge having anopening portion in the case, the loading of the tape is performedaccording to information recorded on the transferred cartridge memory.

FIG. 6 shows a schematic view of a state in which a magnetic tapecartridge having an opening portion formed in a case is mounted on themagnetic recording and reproducing device shown in FIG. 4. An upper partof the magnetic recording and reproducing device may be opened or anopening portion may be provided in the housing H of the magneticrecording and reproducing device so that the displacement of the surfaceof the magnetic tape can be measured by the laser displacement meter.For example, as shown in FIG. 6, the position where the displacement ofthe surface of the magnetic tape is measured by the laser displacementmeter is a rotation angle position where the magnetic tape is notcompletely unwound from the reel (core) of the magnetic tape cartridge.In FIG. 6, a dotted line extending from the laser displacement meterschematically shows a laser beam. The measurement points on the surfaceof the magnetic tape in the width direction are three points of acentral portion in a tape width direction, a portion at 1 mm below anupper edge, and a portion at 1 mm above the lower edge. A width of themagnetic tape is determined according to the standard, for example ½inch. ½ inches=12.65 mm. However, even for magnetic tapes having a widthother than ½ inch, the measurement points in the width direction are theabove three points.

At the time of measurement, a digital oscilloscope, a data logger, orthe like is used to continuously measure the electric signal of thedisplacement of the magnetic tape surface obtained by the laserdisplacement meter and the electric signal of the reel rotation indexobtained by the optical discrimination sensor. The measurement pitch isset as a measurement pitch finer than the reel rotation angle of 1°.

After loading the magnetic tape in the magnetic recording andreproducing device, while winding the magnetic tape around the reel(winding reel 606 in the example shown in FIG. 6) of the magneticrecording and reproducing device at a constant speed in a range of 2m/sec to 8 m/sec by applying a tension in a range of 0.3 N (Newton) to1.1 N in the longitudinal direction, the electric signal of thedisplacement of the surface of the magnetic tape and the electric signalof the rotation index of the reel are measured by using the digitaloscilloscope, the data logger, and the like as described above andstored. The above tension value and speed value are set values in themagnetic recording and reproducing device.

The electric signal of the displacement is converted into a displacementamount (unit: μm) using a coefficient for converting the electric signalof the displacement (voltage value) into a displacement amount, which isdefined for the laser displacement meter used. Such a coefficient isdescribed in, for example, a spec sheet of the laser displacement meter.Using the electric signal of the rotation index of the reel obtained inthe measurement described above, a measurement result used forcalculating the reference circle center position deviation is extractedfrom the measurement results of the displacement amount. Specifically,in a state of being wound around the reel (core) of the magnetic tapecartridge, a terminal of the magnetic tape on the reel side is referredto as an inner terminal, another terminal thereof is referred to as anouter terminal, and one rotation of the core is defined as one period.The measurement result of three continuous rotations (three periods)after a length of approximately 50 m from the outer terminal of themagnetic tape is wound around the reel of the magnetic recording andreproducing device is extracted.

Using the extracted measurement results (displacement amount), for thethree points of the magnetic tape in the width direction, thecalculation of the average minimum region reference circle for onerotation (one period) of the trajectory of the magnetic tape drawn outfrom each core is performed for three rotations (three periods). Theaverage minimum region reference circle is a circle having a radius ofan arithmetic mean of the minimum region reference circle defined inJISB JISB0682-1: 2017 3.3.1.1.3, and is hereinafter, simply referred toas a reference circle. For each of the above three points, thearithmetic mean of the position coordinates of the center position ofthe reference circle for three rotations is defined as a positioncoordinate of the center position of the reference circle at each point.From the position coordinates of the center position of the referencecircle obtained for each of the above three points, the maximum value ofthe deviation of the center position of the average minimum regionreference circle of the above three points (reference circle centerposition deviation) is obtained. That is, the reference circle centerposition deviation is obtained as a distance between two points farthestfrom the center positions of the three reference circles. Ageometrically correct circle is referred to as a geometric circle havinga circular shape, as defined in section 4.3 of JISB0621: 1984. In a casewhere the trajectory of one rotation of the magnetic tape drawn from thecore is a geometric circle, a distance between the laser displacementmeter measured by the laser displacement meter and the measurementposition on the surface of the magnetic tape is constantly the samevalue during one rotation (hereinafter, referred to as X). However, in acase where the trajectory deviates from the geometric circle, thedistance between the laser displacement meter measured by the laserdisplacement meter and the measurement position on the surface of themagnetic tape becomes shorter or longer than X. The difference betweenthis distance and X is the displacement amount measured by the laserdisplacement meter, and from this displacement amount, the trajectory ofone rotation of the magnetic tape drawn from the core can be drawn. Forthe trajectory drawn in this way, the reference circle center positiondeviation is calculated as described above.

In a case where the magnetic tape container is a magnetic recording andreproducing device, the upper part of the magnetic recording andreproducing device is opened or the opening portion of the case of themagnetic recording and reproducing device is provided so that the uppersurface of the flange of the reel and the surface of the magnetic tapeare respectively observed by the optical discrimination sensor and thelaser displacement meter from the outside of the device. By using theunused magnetic recording and reproducing device, except for that themagnetic tape is wound around the other reel from the other reel(winding core) by running the magnetic tape in this magnetic recordingand reproducing device, the reference circle center position deviationis obtained by the method described above using the case where themagnetic tape container is a single reel type magnetic tape cartridge asan example.

In a case where the magnetic tape container is a twin reel type magnetictape cartridge, the opening portion is provided in the magnetic tapecartridge so that the upper surface of the flange of the reel and thesurface of the magnetic tape can be respectively observed by the opticaldiscrimination sensor and the laser displacement meter from the outsideof the case. Except for that the unused twin reel type magnetic tapecartridge is mounted on the magnetic recording and reproducing deviceand the magnetic tape is wound around the other reel from the other reel(core) of the magnetic tape cartridge, the reference circle centerposition deviation is obtained by the method described above using thecase where the magnetic tape container is a single reel type magnetictape cartridge as an example.

Hereinafter, a magnetic tape included in the magnetic tape containerwill be described more specifically.

Existence State of Recesses on Surface of Magnetic Layer

The magnetic tape includes a non-magnetic support, and a magnetic layerincluding a ferromagnetic powder. From the viewpoint of controlling thereference circle center position deviation described above, the numberof recesses having an equivalent circle diameter of 0.20 μm to 0.50 μmexisting on the surface of the magnetic layer is determined. It ispreferable that the number is 10 to 500 per 40 μm×40 μm area.

In the invention and the specification, the number of recesses having anequivalent circle diameter of 0.20 μm to 0.50 μm existing on the surfaceof the magnetic layer is obtained by performing measurement on thesurface of the magnetic layer of the magnetic tape by using an atomicforce microscope (AFM) as will be described below. In the invention andthe specification, the “surface of the magnetic layer” is identical tothe surface of the magnetic tape on the magnetic layer side. The numberof recesses having an equivalent circle diameter of 0.20 μm to 0.50 μmexisting on the surface of the magnetic layer (per 40 μm×40 μm area),which is obtained as will be described below, is also defined as the“number of recesses having an equivalent circle diameter in the aboverange” or simply the “number of recesses”.

A measurement area is a 40 μm square (40 μm×40 μm) region that israndomly selected from the surface of the magnetic layer. Themeasurement is performed at three different measurement points on thesurface of the magnetic layer (n=3). An arithmetic mean of the threemeasurement results obtained by such measurement is defined as thenumber of recesses having an equivalent circle diameter of 0.20 μm to0.50 μm existing on the surface of the magnetic layer of the magnetictape to be measured. In a plane image of the surface of the magneticlayer obtained by using the AFM, a surface of the measurement areaequivalent to volumes of protrusion components and recess components isdefined as a reference surface, and a portion detected as a portionrecessed from this reference surface is specified as a “recess”. Theportion specified as the recess may be a recess, a part of which iswithin the measurement area and the other part of which is beyond themeasurement area. In a case of obtaining the number of recesses, thenumber of recesses is measured by including such a recess. In the planeimage of the surface of the magnetic layer obtained by using the AFM,the area of the portion specified as the recess (hereinafter, “area A”)is measured, and an equivalent circle diameter L is calculated by(A/π){circumflex over ( )}(½)×2=L. Here, an operator “{circumflex over( )}” represents exponentiation. The equivalent circle diameter isobtained as a value in unit of μm and calculated in 0.01 μm incrementsby rounding off three digits after the decimal point and rounding downfour digits after the decimal point. As an example of the measurementcondition of the AFM, the following measurement conditions can be used.

The measurement regarding a region of the surface of the magnetic layerof the magnetic tape having an area of 40 μm×40 μm is performed with anAFM (Nanoscope 5 manufactured by BRUKER Corporation) in a peak forcetapping mode. SCANASYST-AIR manufactured by BRUKER Corporation is usedas a probe, a resolution is set as 512 pixels×512 pixels, and a scanspeed is set by the measurement regarding 1 screen (512 pixels×512pixels) for 512 seconds.

The number of recesses having an equivalent circle diameter of 0.20 μmto 0.50 μm existing on the surface of the magnetic layer of the magnetictape is preferably 10 to 500 per 40 μm×40 μm area. In this regard, thepresent inventors have surmised that the number of recesses having thesize in the range described above existing on the surface of themagnetic layer contribute to enable more evenly drawing the magnetictape in a case of drawing the magnetic tape from the core in themagnetic tape container and/or stabilize a contact state between amagnetic tape transport system (for example, guide or the like) and themagnetic tape, and as a result, it is possible to suppress the positiondeviation in the width direction in the short period described above.From such a viewpoint, the number of recesses having an equivalentcircle diameter in the range described above is preferably 500 or less,more preferably 400 or less, even more preferably 300 or less, and stillpreferably 200 or less. In addition, from such a viewpoint, the numberof recesses having an equivalent circle diameter in the range describedabove is preferably 10 or more, more preferably 50 or more, and evenmore preferably 100 or more.

An example of a method for controlling the number of recesses will bedescribed in detail later.

Curvature of Magnetic Tape in Longitudinal Direction

In one aspect, the curvature of the magnetic tape in the longitudinaldirection is preferably 4 mm/m or less. It is preferable that thecurvature is 4 mm/m or less from the viewpoint of reducing the value ofthe reference circle center position deviation described above. Thecurvature of the magnetic tape in the longitudinal direction is morepreferably 3 mm/m or less, even more preferably 2 mm/m or less, andstill more preferably 1 mm/m or less. The amount of curvature can be 0mm/m or more or more than 0 mm/m, and can also be 0 mm/m. The curvaturecan be controlled by adjusting the manufacturing conditions of themanufacturing step of the magnetic tape. This point will be describedlater in detail.

The curvature of the magnetic tape in the longitudinal direction of thepresent invention and the present specification is a value obtained bythe following method in an environment of an atmosphere temperature of23° C. and a relative humidity of 50%.

FIG. 7 is an explanatory diagram of a curvature of a magnetic tape in alongitudinal direction.

A tape sample having a length of 1 m in a longitudinal direction is cutout from a randomly selected portion of the magnetic tape to bemeasured. The tape sample is hung for 24 hours±4 hours in a tension-freestate by gripping an upper end portion with a gripping member (clip orthe like) by setting the longitudinal direction as the verticaldirection. Then, within 1 hour, the following measurement is performed.

As shown in FIG. 7, the tape piece is placed on a flat surface in atension-free state. The tape piece may be placed on a flat surface withthe surface on the magnetic layer side facing upward, or may be placedon a flat surface with the other surface facing upward. In FIG. 7, Sindicates a tape sample and W indicates the width direction of the tapesample. Using an optical microscope, a distance L (unit: mm) that is ashortest distance between a virtual line 54 connecting both terminalportions 52 and 53 of the tape sample S and a maximum curved portion 55in the longitudinal direction of the tape sample S is measured. FIG. 7shows an example in which the tape sample is curved upward on a papersurface. Even in a case where the tape sample is curved downward, thedistance L (mm) is measured in the same manner. The distance L isdisplayed as a positive value regardless of which side is curved. In acase where no curve in the longitudinal direction is confirmed, the L isset to 0 (zero) mm. The measurement is performed with five differenttape samples, and thus an arithmetic mean of values measured regardingthe tape samples having a length of 1 m is defined as the curvature(unit: mm/m) of the magnetic tape to be measured in the longitudinaldirection.

Vertical Squareness Ratio

In the one embodiment, the vertical squareness ratio of the magnetictape can be, for example, 0.55 or more, and is preferably 0.60 or more.It is preferable that the vertical squareness ratio of the magnetic tapeis 0.60 or more, from a viewpoint of improving the electromagneticconversion characteristics. In principle, an upper limit of thesquareness ratio is 1.00 or less. The vertical squareness ratio of themagnetic tape can be 1.00 or less, 0.95 or less, 0.90 or less, 0.85 orless, or 0.80 or less. It is preferable that the value of the verticalsquareness ratio of the magnetic tape is large from a viewpoint ofimproving the electromagnetic conversion characteristics. The verticalsquareness ratio of the magnetic tape can be controlled by a well-knownmethod such as performing a homeotropic alignment process.

In the invention and the specification, the “vertical squareness ratio”is squareness ratio measured in the vertical direction of the magnetictape. The “vertical direction” described with respect to the squarenessratio is a direction orthogonal to the surface of the magnetic layer,and can also be referred to as a thickness direction. In the inventionand the specification, the vertical squareness ratio is obtained by thefollowing method.

A sample piece having a size that can be introduced into an oscillationsample type magnetic-flux meter is cut out from the magnetic tape to bemeasured. Regarding the sample piece, using the oscillation sample typemagnetic-flux meter, a magnetic field is applied to a vertical directionof a sample piece (direction orthogonal to the surface of the magneticlayer) with a maximum applied magnetic field of 3979 kA/m, a measurementtemperature of 296 K, and a magnetic field sweep speed of 8.3 kA/m/sec,and a magnetization strength of the sample piece with respect to theapplied magnetic field is measured. The measured value of themagnetization strength is obtained as a value after diamagnetic fieldcorrection and a value obtained by subtracting magnetization of a sampleprobe of the oscillation sample type magnetic-flux meter as backgroundnoise. In a case where the magnetization strength at the maximum appliedmagnetic field is Ms and the magnetization strength at zero appliedmagnetic field is Mr, the squareness ratio SQ is a value calculated asSQ=Mr/Ms. The measurement temperature is referred to as a temperature ofthe sample piece, and by setting the ambient temperature around thesample piece to a measurement temperature, the temperature of the samplepiece can be set to the measurement temperature by realizing temperatureequilibrium.

Magnetic Layer Ferromagnetic Powder

As the ferromagnetic powder included in the magnetic layer of themagnetic tape, a well-known ferromagnetic powder can be used as one kindor in combination of two or more kinds as the ferromagnetic powder usedin the magnetic layer of various magnetic recording media. It ispreferable to use a ferromagnetic powder having a small average particlesize as the ferromagnetic powder, from a viewpoint of improvement of arecording density. From this viewpoint, an average particle size of theferromagnetic powder is preferably equal to or smaller than 50 nm, morepreferably equal to or smaller than 45 nm, even more preferably equal toor smaller than 40 nm, further preferably equal to or smaller than 35nm, further more preferably equal to or smaller than 30 nm, further evenmore preferably equal to or smaller than 25 nm, and still preferablyequal to or smaller than 20 nm. Meanwhile, from a viewpoint of stabilityof magnetization, the average particle size of the ferromagnetic powderis preferably equal to or greater than 5 nm, more preferably equal to orgreater than 8 nm, even more preferably equal to or greater than 10 nm,still preferably equal to or greater than 15 nm, and still morepreferably equal to or greater than 20 nm.

Hexagonal Ferrite Powder

As a preferred specific example of the ferromagnetic powder, a hexagonalferrite powder can be used. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the invention and the specification, the “hexagonal ferrite powder”is a ferromagnetic powder in which a hexagonal ferrite type crystalstructure is detected as a main phase by X-ray diffraction analysis. Themain phase is a structure to which a diffraction peak at the highestintensity in an X-ray diffraction spectrum obtained by the X-raydiffraction analysis belongs. For example, in a case where thediffraction peak at the highest intensity in the X-ray diffractionspectrum obtained by the X-ray diffraction analysis belongs to ahexagonal ferrite type crystal structure, it is determined that thehexagonal ferrite type crystal structure is detected as a main phase. Ina case where only a single structure is detected by the X-raydiffraction analysis, this detected structure is set as a main phase.The hexagonal ferrite type crystal structure includes at least an ironatom, a divalent metal atom, and an oxygen atom as constituting atoms. Adivalent metal atom is a metal atom which can be divalent cations asions, and examples thereof include an alkali earth metal atom such as astrontium atom, a barium atom, or a calcium atom, and a lead atom. Inthe invention and the specification, the hexagonal strontium ferritepowder is powder in which a main divalent metal atom included in thispowder is a strontium atom, and the hexagonal barium ferrite powder is apowder in which a main divalent metal atom included in this powder is abarium atom. The main divalent metal atom is a divalent metal atomoccupying the greatest content in the divalent metal atom included inthe powder based on atom %. However, the divalent metal atom describedabove does not include rare earth atom. The “rare earth atom” of theinvention and the specification is selected from the group consisting ofa scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. Thelanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europiumatom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosiumatom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom(Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is oneembodiment of the hexagonal ferrite powder will be described morespecifically.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1,600 nm³. The atomized hexagonalstrontium ferrite powder showing the activation volume in the rangedescribed above is suitable for manufacturing a magnetic tape exhibitingexcellent electromagnetic conversion characteristics. The activationvolume of the hexagonal strontium ferrite powder is preferably equal toor greater than 800 nm³, and can also be, for example, equal to orgreater than 850 nm³. In addition, from a viewpoint of further improvingthe electromagnetic conversion characteristics, the activation volume ofthe hexagonal strontium ferrite powder is more preferably equal to orsmaller than 1,500 nm³, even more preferably equal to or smaller than1,400 nm³, still preferably equal to or smaller than 1,300 nm³, stillmore preferably equal to or smaller than 1,200 nm³, and still even morepreferably equal to or smaller than 1,100 nm³. The same applies to theactivation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and anindicator showing a magnetic magnitude of the particles. Regarding theactivation volume and an anisotropy constant Ku which will be describedlater disclosed in the invention and the specification, magnetic fieldsweep rates of a coercivity Hc measurement part at time points of 3minutes and 30 minutes are measured by using an oscillation sample typemagnetic-flux meter (measurement temperature: 23° C.±1° C.), and theactivation volume and the anisotropy constant Ku are values acquiredfrom the following relational expression of Hc and an activation volumeV. A unit of the anisotropy constant Ku is 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant (unit: J/m³), Ms: saturationmagnetization (unit: kA/m), k: Boltzmann's constant, T: absolutetemperature (unit: K), V: activation volume (unit: cm³), A: spinprecession frequency (unit: s⁻¹), and t: magnetic field reversal time(unit: s)]

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Thehexagonal strontium ferrite powder can preferably have Ku equal to orgreater than 1.8×10⁵ J/m³, and more preferably have Ku equal to orgreater than 2.0×10⁵ J/m³. In addition, Ku of the hexagonal strontiumferrite powder can be, for example, equal to or smaller than 2.5×10⁵J/m³. However, the high Ku is preferable, because it means high thermalstability, and thus, Ku is not limited to the exemplified value.

The hexagonal strontium ferrite powder may or may not include the rareearth atom. In a case where the hexagonal strontium ferrite powderincludes the rare earth atom, a content (bulk content) of the rare earthatom is preferably 0.5 to 5.0 atom % with respect to 100 atom % of theiron atom. In the one embodiment, the hexagonal strontium ferrite powderincluding the rare earth atom can have a rare earth atom surface layerportion uneven distribution. The “rare earth atom surface layer portionuneven distribution” of the invention and the specification means that acontent of rare earth atom with respect to 100 atom % of iron atom in asolution obtained by partially dissolving the hexagonal strontiumferrite powder with acid (hereinafter, referred to as a “rare earth atomsurface layer portion content” or simply a “surface layer portioncontent” regarding the rare earth atom) and a content of rare earth atomwith respect to 100 atom % of iron atom in a solution obtained bytotally dissolving the hexagonal strontium ferrite powder with acid(hereinafter, referred to as a “rare earth atom bulk content” or simplya “bulk content” regarding the rare earth atom) satisfy a ratio of rareearth atom surface layer portion content/rare earth atom bulk content>1.0.

The content of rare earth atom of the hexagonal strontium ferrite powderwhich will be described later is identical to the rare earth atom bulkcontent. With respect to this, the partial dissolving using acid is todissolve the surface layer portion of particles configuring thehexagonal strontium ferrite powder, and accordingly, the content of rareearth atom in the solution obtained by the partial dissolving is thecontent of rare earth atom in the surface layer portion of the particlesconfiguring the hexagonal strontium ferrite powder. The rare earth atomsurface layer portion content satisfying a ratio of “rare earth atomsurface layer portion content/rare earth atom bulk content >1.0” meansthat the rare earth atoms are unevenly distributed in the surface layerportion (that is, a larger amount of the rare earth atoms is present,compared to that inside), among the particles configuring the hexagonalstrontium ferrite powder. The surface layer portion of the invention andthe specification means a part of the region of the particlesconfiguring the hexagonal strontium ferrite powder towards the insidefrom the surface.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, a content (bulk content) of the rare earth atom ispreferably 0.5 to 5.0 atom % with respect to 100 atom % of the ironatom. It is thought that the rare earth atom having the bulk content inthe range described above and uneven distribution of the rare earth atomin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder contribute to the prevention of a decrease inreproducing output during the repeated reproducing. It is surmised thatthis is because the rare earth atom having the bulk content in the rangedescribed above included in the hexagonal strontium ferrite powder andthe uneven distribution of the rare earth atom in the surface layerportion of the particles configuring the hexagonal strontium ferritepowder can increase the anisotropy constant Ku. As the value of theanisotropy constant Ku is high, occurrence of a phenomenon calledthermal fluctuation (that is, improvement of thermal stability) can beprevented. By preventing the occurrence of the thermal fluctuation, adecrease in reproducing output during the repeated reproducing can beprevented. It is surmised that the uneven distribution of the rare earthatom in the surface layer portion of the particles of the hexagonalstrontium ferrite powder contributes to stabilization of a spin at aniron (Fe) site in a crystal lattice of the surface layer portion,thereby increasing the anisotropy constant Ku.

In addition, it is surmised that the use of the hexagonal strontiumferrite powder having the rare earth atom surface layer portion unevendistribution as the ferromagnetic powder of the magnetic layer alsocontributes to the prevention of chipping of the surface of the magneticlayer due to the sliding with the magnetic head. That is, it is surmisedthat, the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution can also contribute to theimprovement of running durability of the magnetic tape. It is surmisedthat this is because the uneven distribution of the rare earth atom onthe surface of the particles configuring the hexagonal strontium ferritepowder contributes to improvement of an interaction between the surfaceof the particles and an organic substance (for example, binding agentand/or additive) included in the magnetic layer, thereby improvingstrength of the magnetic layer.

From a viewpoint of even more preventing reduction of the reproductionoutput in the repeated reproduction and/or a viewpoint of furtherimproving running durability, the content of rare earth atom (bulkcontent) is more preferably in a range of 0.5 to 4.5 atom %, even morepreferably in a range of 1.0 to 4.5 atom %, and still preferably in arange of 1.5 to 4.5 atom %.

The bulk content is a content obtained by totally dissolving thehexagonal strontium ferrite powder. In the invention and thespecification, the content of the atom is a bulk content obtained bytotally dissolving the hexagonal strontium ferrite powder, unlessotherwise noted. The hexagonal strontium ferrite powder including therare earth atom may include only one kind of rare earth atom or mayinclude two or more kinds of rare earth atom, as the rare earth atom. Ina case where two or more kinds of rare earth atom are included, the bulkcontent is obtained from the total of the two or more kinds of rareearth atom. The same also applies to the other components of theinvention and the specification. That is, for a given component, onlyone kind may be used or two or more kinds may be used, unless otherwisenoted. In a case where two or more kinds are used, the content is acontent of the total of the two or more kinds.

In a case where the hexagonal strontium ferrite powder includes the rareearth atom, the rare earth atom included therein may be any one or morekinds of the rare earth atom. Examples of the rare earth atom preferablefrom a viewpoint of even more preventing reduction of the reproductionoutput during the repeated reproduction include a neodymium atom, asamarium atom, an yttrium atom, and a dysprosium atom, a neodymium atom,a samarium atom, an yttrium atom are more preferable, and a neodymiumatom is even more preferable.

In the hexagonal strontium ferrite powder having the rare earth atomsurface layer portion uneven distribution, a degree of unevendistribution of the rare earth atom is not limited, as long as the rareearth atom is unevenly distributed in the surface layer portion of theparticles configuring the hexagonal strontium ferrite powder. Forexample, regarding the hexagonal strontium ferrite powder having therare earth atom surface layer portion uneven distribution, a ratio ofthe surface layer portion content of the rare earth atom obtained bypartial dissolving performed under the dissolving conditions which willbe described later and the bulk content of the rare earth atom obtainedby total dissolving performed under the dissolving conditions which willbe described later, “surface layer portion content/bulk content” isgreater than 1.0 and can be equal to or greater than 1.5. The “surfacelayer portion content/bulk content” greater than 1.0 means that the rareearth atoms are unevenly distributed in the surface layer portion (thatis, a larger amount of the rare earth atoms is present, compared to thatinside), in the particles configuring the hexagonal strontium ferritepowder. A ratio of the surface layer portion content of the rare earthatom obtained by partial dissolving performed under the dissolvingconditions which will be described later and the bulk content of therare earth atom obtained by total dissolving performed under thedissolving conditions which will be described later, “surface layerportion content/bulk content” can be, for example, equal to or smallerthan 10.0, equal to or smaller than 9.0, equal to or smaller than 8.0,equal to or smaller than 7.0, equal to or smaller than 6.0, equal to orsmaller than 5.0, or equal to or smaller than 4.0. However, in thehexagonal strontium ferrite powder having the rare earth atom surfacelayer portion uneven distribution, the “surface layer portioncontent/bulk content” is not limited to the exemplified upper limit orthe lower limit, as long as the rare earth atom is unevenly distributedin the surface layer portion of the particles configuring the hexagonalstrontium ferrite powder.

The partial dissolving and the total dissolving of the hexagonalstrontium ferrite powder will be described below. Regarding thehexagonal strontium ferrite powder present as the powder, sample powderfor the partial dissolving and the total dissolving are collected frompowder of the same batch. Meanwhile, regarding the hexagonal strontiumferrite powder included in a magnetic layer of a magnetic tape, a partof the hexagonal strontium ferrite powder extracted from the magneticlayer is subjected to the partial dissolving and the other part issubjected to the total dissolving. The extraction of the hexagonalstrontium ferrite powder from the magnetic layer can be performed by,for example, a method disclosed in a paragraph 0032 of JP2015-91747A.

The partial dissolving means dissolving performed so that the hexagonalstrontium ferrite powder remaining in the solution can be visuallyconfirmed in a case of the completion of the dissolving. For example, byperforming the partial dissolving, a region of the particles configuringthe hexagonal strontium ferrite powder which is 10% to 20% by mass withrespect to 100% by mass of a total of the particles can be dissolved. Onthe other hand, the total dissolving means dissolving performed untilthe hexagonal strontium ferrite powder remaining in the solution is notvisually confirmed in a case of the completion of the dissolving.

The partial dissolving and the measurement of the surface layer portioncontent are, for example, performed by the following method. However,dissolving conditions such as the amount of sample powder and the likedescribed below are merely examples, and dissolving conditions capableof performing the partial dissolving and the total dissolving can berandomly used.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 1 mol/L is held on ahot plate at a set temperature of 70° C. for 1 hour. The obtainedsolution is filtered with a membrane filter having a hole diameter of0.1 μm. The element analysis of the filtrate obtained as described aboveis performed by an inductively coupled plasma (ICP) analysis device. Bydoing so, the surface layer portion content of the rare earth atom withrespect to 100 atom % of the iron atom can be obtained. In a case wherea plurality of kinds of rare earth atoms are detected from the elementanalysis, a total content of the entirety of the rare earth atoms is thesurface layer portion content. The same applies to the measurement ofthe bulk content.

Meanwhile, the total dissolving and the measurement of the bulk contentare, for example, performed by the following method.

A vessel (for example, beaker) containing 12 mg of sample powder and 10mL of hydrochloric acid having a concentration of 4 mol/L is held on ahot plate at a set temperature of 80° C. for 3 hours. After that, theprocess is performed in the same manner as in the partial dissolving andthe measurement of the surface layer portion content, and the bulkcontent with respect to 100 atom % of the iron atom can be obtained.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regards to this point, in hexagonal strontium ferritepowder which includes the rare earth atom but does not have the rareearth atom surface layer portion uneven distribution, σs tends tosignificantly decrease, compared to that in hexagonal strontium ferritepowder not including the rare earth atom. With respect to this, it isthought that, hexagonal strontium ferrite powder having the rare earthatom surface layer portion uneven distribution is also preferable forpreventing such a significant decrease in σs. In one embodiment, σs ofthe hexagonal strontium ferrite powder can be equal to or greater than45 A×m²/kg and can also be equal to or greater than 47 A×m²/kg. On theother hand, from a viewpoint of noise reduction, σs is preferably equalto or smaller than 80 A×m²/kg and more preferably equal to or smallerthan 60 A×m²/kg. σs can be measured by using a well-known measurementdevice capable of measuring magnetic properties such as an oscillationsample type magnetic-flux meter. In the invention and the specification,the mass magnetization σs is a value measured at a magnetic fieldstrength of 15 kOe, unless otherwise noted. 1[kOe]=(10⁶/4π) [A/m]

Regarding the content (bulk content) of the constituting atom in thehexagonal strontium ferrite powder, a content of the strontium atom canbe, for example, 2.0 to 15.0 atom % with respect to 100 atom % of theiron atom. In one embodiment, in the hexagonal strontium ferrite powder,the divalent metal atom included in this powder can be only a strontiumatom. In another embodiment, the hexagonal strontium ferrite powder canalso include one or more kinds of other divalent metal atoms, inaddition to the strontium atom. For example, the hexagonal strontiumferrite powder can include a barium atom and/or a calcium atom. In acase where the other divalent metal atom other than the strontium atomis included, a content of a barium atom and a content of a calcium atomin the hexagonal strontium ferrite powder respectively can be, forexample, 0.05 to 5.0 atom % with respect to 100 atom % of the iron atom.

As the crystal structure of the hexagonal ferrite, a magnetoplumbitetype (also referred to as an “M type”), a W type, a Y type, and a Z typeare known. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be confirmed by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more kinds of crystal structure can be detected bythe X-ray diffraction analysis. For example, in one embodiment, in thehexagonal strontium ferrite powder, only the M type crystal structurecan be detected by the X-ray diffraction analysis. For example, the Mtype hexagonal ferrite is represented by a compositional formula ofAFe₁₂O₁₉. Here, A represents a divalent metal atom, in a case where thehexagonal strontium ferrite powder has the M type, A is only a strontiumatom (Sr), or in a case where a plurality of divalent metal atoms areincluded as A, the strontium atom (Sr) occupies the hexagonal strontiumferrite powder with the greatest content based on atom % as describedabove. A content of the divalent metal atom in the hexagonal strontiumferrite powder is generally determined according to the type of thecrystal structure of the hexagonal ferrite and is not particularlylimited. The same applies to a content of an iron atom and a content ofan oxygen atom. The hexagonal strontium ferrite powder at least includesan iron atom, a strontium atom, and an oxygen atom, and can also includea rare earth atom. In addition, the hexagonal strontium ferrite powdermay or may not include atoms other than these atoms. As an example, thehexagonal strontium ferrite powder may include an aluminum atom (Al). Acontent of the aluminum atom can be, for example, 0.5 to 10.0 atom %with respect to 100 atom % of the iron atom. From a viewpoint of evenmore preventing the reduction of the reproduction output during therepeated reproduction, the hexagonal strontium ferrite powder includesthe iron atom, the strontium atom, the oxygen atom, and the rare earthatom, and a content of the atoms other than these atoms is preferablyequal to or smaller than 10.0 atom %, more preferably 0 to 5.0 atom %,and may be 0 atom % with respect to 100 atom % of the iron atom. Thatis, in one embodiment, the hexagonal strontium ferrite powder may notinclude atoms other than the iron atom, the strontium atom, the oxygenatom, and the rare earth atom. The content shown with atom % describedabove is obtained by converting a value of the content (unit: % by mass)of each atom obtained by totally dissolving the hexagonal strontiumferrite powder into a value shown as atom % by using the atomic weightof each atom. In addition, in the invention and the specification, agiven atom which is “not included” means that the content thereofobtained by performing total dissolving and measurement by using an ICPanalysis device is 0% by mass. A detection limit of the ICP analysisdevice is generally equal to or smaller than 0.01 ppm (parts permillion) based on mass. The expression “not included” is used as ameaning including that a given atom is included with the amount smallerthan the detection limit of the ICP analysis device. In one embodiment,the hexagonal strontium ferrite powder does not include a bismuth atom(Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, an ε-ironoxide powder can also be used. In the invention and the specification,the “ε-iron oxide powder” is a ferromagnetic powder in which an ε-ironoxide type crystal structure is detected as a main phase by X-raydiffraction analysis. For example, in a case where the diffraction peakat the highest intensity in the X-ray diffraction spectrum obtained bythe X-ray diffraction analysis belongs to an ε-iron oxide type crystalstructure, it is determined that the ε-iron oxide type crystal structureis detected as a main phase. As a manufacturing method of the ε-ironoxide powder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. For the method of manufacturing the ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. 51, pp. S280-S284, J. Mater. Chem. C,2013, 1, pp.5200-5206 can be referred, for example. However, themanufacturing method of the ε-iron oxide powder capable of being used asthe ferromagnetic powder in the magnetic layer of the magnetic tape isnot limited to the method described here.

An activation volume of the ε-iron oxide powder is preferably 300 to1,500 nm³. The atomized ε-iron oxide powder showing the activationvolume in the range described above is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. The activation volume of the ε-iron oxide powder ispreferably equal to or greater than 300 nm³, and can also be, forexample, equal to or greater than 500 nm³. In addition, from a viewpointof further improving the electromagnetic conversion characteristics, theactivation volume of the ε-iron oxide powder is more preferably equal toor smaller than 1,400 nm³, even more preferably equal to or smaller than1,300 nm³, still preferably equal to or smaller than 1,200 nm³, andstill more preferably equal to or smaller than 1,100 nm³.

The anisotropy constant Ku can be used as an index of reduction ofthermal fluctuation, that is, improvement of thermal stability. Theε-iron oxide powder can preferably have Ku equal to or greater than3.0×10⁴ J/m³, and more preferably have Ku equal to or greater than8.0×10⁴ J/m³. In addition, Ku of the ε-iron oxide powder can be, forexample, equal to or smaller than 3.0×10⁵ J/m³. However, the high Ku ispreferable, because it means high thermal stability, and thus, Ku is notlimited to the exemplified value.

From a viewpoint of increasing reproducing output in a case ofreproducing data recorded on a magnetic tape, it is desirable that themass magnetization σs of ferromagnetic powder included in the magnetictape is high. In regard to this point, in one embodiment, σs of theε-iron oxide powder can be equal to or greater than 8 A×m²/kg and canalso be equal to or greater than 12 A×m²/kg. On the other hand, from aviewpoint of noise reduction, σs of the ε-iron oxide powder ispreferably equal to or smaller than 40 A×m²/kg and more preferably equalto or smaller than 35 A×m²/kg.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at an imaging magnification ratio of 100,000 with atransmission electron microscope, the image is printed onto aphotographic printing paper so that a total magnification ratio of500,000 of an image of particles configuring the powder is obtained. Atarget particle is selected from the obtained image of particles, anoutline of the particle is traced with a digitizer, and a size of theparticle (primary particle) is measured. The primary particle is anindependent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetic mean of the particle size of 500particles obtained as described above is the average particle size ofthe powder. As the transmission electron microscope, a transmissionelectron microscope H-9000 manufactured by Hitachi, Ltd. can be used,for example. In addition, the measurement of the particle size can beperformed by a well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an embodiment in which particles configuringthe aggregate are directly in contact with each other, but also includesan embodiment in which a binding agent or an additive which will bedescribed later is interposed between the particles. A term, particlesmay be used for representing the powder.

As a method for collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted,

(1) in a case where the shape of the particle observed in the particleimage described above is a needle shape, a fusiform shape, or a columnarshape (here, a height is greater than a maximum long diameter of abottom surface), the size (particle size) of the particles configuringthe powder is shown as a length of a major axis configuring theparticle, that is, a major axis length,

(2) in a case where the shape of the particle is a planar shape or acolumnar shape (here, a thickness or a height is smaller than a maximumlong diameter of a plate surface or a bottom surface), the particle sizeis shown as a maximum long diameter of the plate surface or the bottomsurface, and

(3) in a case where the shape of the particle is a sphere shape, apolyhedron shape, or an unspecified shape, and the major axisconfiguring the particles cannot be specified from the shape, theparticle size is shown as an equivalent circle diameter. The equivalentcircle diameter is a value obtained by a circle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a minor axis, that is, a minor axis length of the particles ismeasured in the measurement described above, a value of (major axislength/minor axis length) of each particle is obtained, and anarithmetic mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the minoraxis length as the definition of the particle size is a length of aminor axis configuring the particle, in a case of (2), the minor axislength is a thickness or a height, and in a case of (3), the major axisand the minor axis are not distinguished, thus, the value of (major axislength/minor axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average major axislength, and in a case of the same definition (2), the average particlesize is an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50% to 90% by mass and more preferably 60%to 90% by mass with respect to a total mass of the magnetic layer. Ahigh filling percentage of the ferromagnetic powder in the magneticlayer is preferable from a viewpoint of improvement of recordingdensity.

Binding Agent

The magnetic tape may be a coating type magnetic tape, and can include abinding agent in the magnetic layer. The binding agent is one or morekinds of resin. As the binding agent, various resins normally used as abinding agent of a coating type magnetic tape can be used. As thebinding agent, a resin selected from a polyurethane resin, a polyesterresin, a polyamide resin, a vinyl chloride resin, an acrylic resinobtained by copolymerizing styrene, acrylonitrile, or methylmethacrylate, a cellulose resin such as nitrocellulose, an epoxy resin,a phenoxy resin, and a polyvinylalkylal resin such as polyvinyl acetalor polyvinyl butyral can be used alone or a plurality of resins can bemixed with each other to be used. Among these, a polyurethane resin, anacrylic resin, a cellulose resin, and a vinyl chloride resin arepreferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the non-magnetic layerand/or a back coating layer which will be described later.

For the binding agent described above, descriptions disclosed inparagraphs 0028 to 0031 of JP2010-24113A can be referred to. An averagemolecular weight of the resin used as the binding agent can be, forexample, 10,000 to 200,000 as a weight-average molecular weight. Theamount of the binding agent used can be, for example, 1.0 to 30.0 partsby mass with respect to 100.0 parts by mass of the ferromagnetic powder.

Curing Agent

A curing agent can also be used together with the resin which can beused as the binding agent. As the curing agent, in one embodiment, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother embodiment, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinding agent, by proceeding the curing reaction in the magnetic layerforming step. This point is the same as regarding a layer formed byusing a composition, in a case where the composition used for formingthe other layer includes the curing agent. The preferred curing agent isa thermosetting compound, and polyisocyanate is suitable. For thedetails of polyisocyanate, descriptions disclosed in paragraphs 0124 and0125 of JP2011-216149A can be referred to. The amount of the curingagent can be, for example, 0 to 80.0 parts by mass with respect to 100.0parts by mass of the binding agent in the magnetic layer formingcomposition, and is preferably 50.0 to 80.0 parts by mass, from aviewpoint of improvement of hardness of the magnetic layer.

Additives

The magnetic layer may include one or more kinds of additives, asnecessary. As the additives, a commercially available product can besuitably selected and used according to the desired properties.Alternatively, a compound synthesized by a well-known method can be usedas the additives. The additive can be used with a random amount. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive included in the magnetic layerinclude a non-magnetic powder (for example, inorganic powder, carbonblack, or the like), a lubricant, a dispersing agent, a dispersingassistant, a fungicide, an antistatic agent, and an antioxidant. Forexample, for the lubricant, a description disclosed in paragraphs 0030to 0033, 0035, and 0036 of JP2016-126817A can be referred to. Thelubricant may be included in the non-magnetic layer which will bedescribed later. For the lubricant which may be included in thenon-magnetic layer, a description disclosed in paragraphs 0030, 0031,0034, 0035, and 0036 of JP2016-126817A can be referred to. For thedispersing agent, a description disclosed in paragraphs 0061 and 0071 ofJP2012-133837A can be referred to. The dispersing agent may be added toa non-magnetic layer forming composition. For the dispersing agent whichcan be added to the non-magnetic layer forming composition, adescription disclosed in paragraph 0061 of JP2012-133837A can bereferred to. As the non-magnetic powder which may be included in themagnetic layer, non-magnetic powder which can function as an abrasive,non-magnetic powder (for example, non-magnetic colloid particles) whichcan function as a projection formation agent which forms projectionssuitably protruded from the surface of the magnetic layer, and the likecan be used. For example, for the abrasive, a description disclosed inparagraphs 0030 to 0032 of JP2004-273070A can be referred to. As theprojection formation agent, colloidal particles are preferable, and froma viewpoint of availability, inorganic colloidal particles arepreferable, inorganic oxide colloidal particles are more preferable, andsilica colloidal particles (colloidal silica) are even more preferable.Average particle sizes of the abrasive and the projection formationagent are respectively preferably 30 to 200 nm and more preferably 50 to100 nm.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on the surface of the non-magneticsupport or may include a magnetic layer on the surface of thenon-magnetic support through the non-magnetic layer including thenon-magnetic powder. The non-magnetic powder used in the non-magneticlayer may be a powder of an inorganic substance or a powder of anorganic substance. In addition, carbon black and the like can be used.Examples of powder of the inorganic substance include powder of metal,metal oxide, metal carbonate, metal sulfate, metal nitride, metalcarbide, and metal sulfide. The non-magnetic powder can be purchased asa commercially available product or can be manufactured by a well-knownmethod. For details thereof, descriptions disclosed in paragraphs 0146to 0150 of JP2011-216149A can be referred to. For carbon black which canbe used in the non-magnetic layer, descriptions disclosed in paragraphs0040 and 0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably 50% to 90% by mass and more preferably 60% to 90% by masswith respect to a total mass of the non-magnetic layer.

The non-magnetic layer can include a binding agent and can also includeadditives. In regards to other details of a binding agent and additivesof the non-magnetic layer, the well-known technology regarding thenon-magnetic layer can be applied. In addition, in regards to the typeand the content of the binding agent, and the type and the content ofthe additive, for example, the well-known technology regarding themagnetic layer can be applied.

The non-magnetic layer of the invention and the specification alsoincludes a substantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

As the non-magnetic support (hereinafter, also simply referred to as a“support”), well-known components such as polyethylene terephthalate,polyethylene naphthalate, polyamide, polyamide imide, aromatic polyamidesubjected to biaxial stretching are used. Among these, polyethyleneterephthalate and polyethylene naphthalate, are preferable.

In the one embodiment, the non-magnetic support of the magnetic tape canbe an aromatic polyester support. In the invention and thespecification, “aromatic polyester” means a resin including an aromaticskeleton and a plurality of ester bonds, and the “aromatic polyestersupport” means a support including at least one layer of an aromaticpolyester film. The “aromatic polyester film” is a film in which thelargest component in the component configuring this film based on massis aromatic polyester. The “aromatic polyester support” of the inventionand the specification include a support in which all of resin filmsincluded in this support is the aromatic polyester film and a supportincluding the aromatic polyester film and the other resin film. Specificexamples of the aromatic polyester support include a single aromaticpolyester film, a laminated film of two or more layers of the aromaticpolyester film having the same constituting component, a laminated filmof two or more layers of the aromatic polyester film having differentconstituting components, and a laminated film including one or morelayers of the aromatic polyester film and one or more layers of resinfilm other than the aromatic polyester. In the laminated film, anadhesive layer or the like may be randomly included between two adhesivelayers. In addition, the aromatic polyester support may randomly includea metal film and/or a metal oxide film formed by performing vapordeposition or the like on one or both surfaces. The same applies to a“polyethylene terephthalate support” and a “polyethylene naphthalatesupport” in the invention and the specification.

An aromatic ring included in an aromatic skeleton including the aromaticpolyester is not particularly limited. Specific examples of the aromaticring include a benzene ring and naphthalene ring.

For example, polyethylene terephthalate (PET) is polyester including abenzene ring, and is a resin obtained by polycondensation of ethyleneglycol and terephthalic acid and/or dimethyl terephthalate. The“polyethylene terephthalate” of the invention and the specificationincludes polyethylene terephthalate having a structure including one ormore kinds of other components (for example, copolymerization component,and component introduced to a terminal or a side chain), in addition tothe component described above.

Polyethylene naphthalate (PEN) is polyester including a naphthalenering, and is a resin obtained by performing esterification reaction ofdimethyl 2,6-naphthalenedicarboxylate and ethylene glycol, and then,transesterification and polycondensation reaction. The “polyethylenenaphthalate” of the invention and the specification includespolyethylene naphthalate having a structure including one or more kindsof other components (for example, copolymerization component, andcomponent introduced to a terminal or a side chain), in addition to thecomponent described above.

In addition, the non-magnetic support can be a biaxial stretching film,and may be a film subjected to corona discharge, plasma treatment, easyadhesion treatment, heat treatment, or the like.

Back Coating Layer

The magnetic tape may or may not include a back coating layer includinga non-magnetic powder on a surface side of the non-magnetic supportopposite to the surface side provided with the magnetic layer. For thenon-magnetic powder of the back coating layer, the above descriptionregarding the non-magnetic powder of the non-magnetic layer can bereferred to.

In a manufacturing step and the like of the magnetic tape, the surfaceshape of the rear surface is transferred to the surface of the magneticlayer (so-called offset) while the front surface and the rear surface ofthe magnetic layer are in contact with each other in a rolled state,thereby forming a recess on the surface of the magnetic layer. The rearsurface is the surface of the back coating layer in a case of includingthe back coating layer, is a surface of the support in a case of notincluding the back coating layer. As an example of a method forcontrolling the existence state of recess on the surface of the magneticlayer, a type of component to be added to the composition for formingthe back coating layer, for example, can be selected, in order to adjustthe surface shape of the rear surface. From this viewpoint, as thenon-magnetic powder of the back coating layer, it is preferable thatcarbon black and a non-magnetic powder other than carbon black are usedin combination, or carbon black is used (that is, the non-magneticpowder of the back coating layer consists of carbon black). Examples ofthe non-magnetic powder other than carbon black include the non-magneticpowder exemplified above as one that can be contained in thenon-magnetic layer. Regarding the non-magnetic powder of the backcoating layer, a percentage of carbon black with respect to 100.0 partsby mass of the total amount of the non-magnetic powder is preferably ina range of 50.0 to 100.0 parts by mass, more preferably in a range of70.0 to 100.0 parts by mass, even more preferably in a range of 90.0 to100.0 parts by mass. In addition, it is also preferable that the totalamount of the non-magnetic powder in the back coating layer is carbonblack. The content (filling percentage) of the non-magnetic powder inthe back coating layer is preferably in a range of 50 to 90% by mass andmore preferably in a range of 60 to 90% by mass, with respect to thetotal mass of the back coating layer.

From a viewpoint of ease of control of the number of recesses having theequivalent circle diameter in the range described above existing on thesurface of the magnetic layer, in the one embodiment, a non-magneticpowder having an average particle size of 50 nm or less is preferablyused as the non-magnetic powder of the back coating layer. As thenon-magnetic powder of the back coating layer, only one kind of thenon-magnetic powder may be used or two or more kinds thereof may beused. In a case of using two or more kinds (for example, carbon blackand a non-magnetic powder other than carbon black), the average particlesize of each is preferably 50 nm or less. The average particle size ofthe non-magnetic powder is more preferably in a range of 10 to 50 nm andeven more preferably in a range of 10 to 30 nm. In the one embodiment, atotal amount of the non-magnetic powder contained in the back coatinglayer is preferably carbon black and the average particle size thereofis more preferably 50 nm or less.

In order to control the existence state of the recesses on the surfaceof the magnetic layer, the back coating layer forming compositionpreferably contains a component (dispersing agent) capable of increasingthe dispersibility of the non-magnetic powder contained in thiscomposition. The back coating layer forming composition more preferablycontains a non-magnetic powder having an average particle size of 50 nmor less and a component capable of increasing dispersibility of thisnon-magnetic powder, and even more preferably contains carbon blackhaving an average particle size of 50 nm or less and a component capableof increasing the dispersibility of carbon black.

As an example of such a dispersing agent, a compound having an ammoniumsalt structure of an alkyl ester anion represented by Formula 1 can beused. The “alkyl ester anion” can also be referred to as an “alkylcarboxylate anion”.

In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms, and Z⁺represents an ammonium cation.

In addition, from a viewpoint of improving the dispersibility of carbonblack, in the one embodiment, two or more kinds of components capable offorming the compound having a salt structure can be used in a case ofpreparing the back coating layer forming composition. Accordingly, in acase of preparing the back coating layer forming composition, at leastsome of these components can form the compound having the saltstructure.

Unless otherwise noted, groups described below may have a substituent ormay be unsubstituted. In addition, the “number of carbon atoms” of agroup having a substituent means the number of carbon atoms notincluding the number of carbon atoms of the substituent, unlessotherwise noted. In the present invention and the specification,examples of the substituent include an alkyl group (for example, analkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxygroup (for example, an alkoxy group having 1 to 6 carbon atoms), ahalogen atom (for example, a fluorine atom, a chlorine atom, a bromineatom, or the like), a cyano group, an amino group, a nitro group, anacyl group, a carboxy group, salt of a carboxy group, a sulfonic acidgroup, and salt of a sulfonic acid group.

Hereinafter, Formula 1 will be described in more detail.

In Formula 1, R represents an alkyl group having 7 or more carbon atomsor a fluorinated alkyl group having 7 or more carbon atoms. Thefluorinated alkyl group has a structure in which some or all of thehydrogen atoms constituting the alkyl group are substituted with afluorine atom. The alkyl group or fluorinated alkyl group represented byR may have a linear structure, a branched structure, may be a cyclicalkyl group or fluorinated alkyl group, and preferably has a linearstructure. The alkyl group or fluorinated alkyl group represented by Rmay have a substituent, may be unsubstituted, and is preferablyunsubstituted. The alkyl group represented by R can be represented by,for example, C_(n)H_(2n+1)—. Here, n represents an integer of 7 or more.In addition, for example, the fluorinated alkyl group represented by Rmay have a structure in which a part or all of the hydrogen atomsconstituting the alkyl group represented by C_(n)H_(2n+1)— aresubstituted with a fluorine atom. The alkyl group or fluorinated alkylgroup represented by R has 7 or more carbon atoms, preferably 8 or morecarbon atoms, more preferably 9 or more carbon atoms, further preferably10 or more carbon atoms, still preferably 11 or more carbon atoms, stillmore preferably 12 or more carbon atoms, and still even more preferably13 or more carbon atoms. The alkyl group or fluorinated alkyl grouprepresented by R has preferably 20 or less carbon atoms, more preferably19 or less carbon atoms, and even more preferably 18 or less carbonatoms.

In Formula 1, Z⁺ represents an ammonium cation. Specifically, theammonium cation has the following structure. In the present inventionand the present specification, “*” in the formulas that represent a partof the compound represents a bonding position between the structure ofthe part and the adjacent atom.

The nitrogen cation N⁺ of the ammonium cation and the oxygen anion O⁻ inFormula 1 may form a salt bridging group to form the ammonium saltstructure of the alkyl ester anion represented by Formula 1. The factthat the compound having the ammonium salt structure of the alkyl esteranion represented by Formula 1 is contained in the back coating layercan be confirmed by performing analysis with respect to the magnetictape by X-ray photoelectron spectroscopy (electron spectroscopy forchemical analysis (ESCA)), infrared spectroscopy (IR), or the like.

In the one embodiment, the ammonium cation represented by Z⁺ can beprovided by, for example, the nitrogen atom of the nitrogen-containingpolymer becoming a cation. The nitrogen-containing polymer means apolymer containing a nitrogen atom. In the present invention and thepresent specification, a term “polymer” means to include both ahomopolymer and a copolymer. The nitrogen atom can be included as anatom configuring a main chain of the polymer in one embodiment, and canbe included as an atom constituting a side chain of the polymer in oneembodiment.

As one embodiment of the nitrogen-containing polymer, polyalkyleneiminecan be used. The polyalkyleneimine is a ring-opening polymer ofalkyleneimine and is a polymer having a plurality of repeating unitsrepresented by Formula 2.

The nitrogen atom N configuring the main chain in Formula 2 can beconverted to a nitrogen cation N⁺ to provide an ammonium cationrepresented by Z⁺ in Formula 1. Then, an ammonium salt structure can beformed with the alkyl ester anion, for example, as follows.

Hereinafter, Formula 2 will be described in more detail.

In Formula 2, R¹ and R² each independently represent a hydrogen atom oran alkyl group, and n1 represents an integer of 2 or more.

Examples of the alkyl group represented by R¹ or R² include an alkylgroup having 1 to 6 carbon atoms, preferably an alkyl group having 1 to3 carbon atoms, more preferably a methyl group or an ethyl group, andeven more preferably a methyl group. The alkyl group represented by R¹or R² is preferably an unsubstituted alkyl group. A combination of R¹and R² in Formula 2 is a form in which one is a hydrogen atom and theother is an alkyl group, a form in which both are hydrogen atoms, and aform in which both are an alkyl group (the same or different alkylgroups), and is preferably a form in which both are hydrogen atoms. Asthe alkyleneimine that provides the polyalkyleneimine, a structure ofthe ring that has the smallest number of carbon atoms is ethyleneimine,and the main chain of the alkyleneimine (ethyleneimine) obtained by ringopening of ethyleneimine has 2 carbon atoms. Accordingly, n1 in Formula2 is 2 or more. n1 in Formula 2 can be, for example, 10 or less, 8 orless, 6 or less, or 4 or less. The polyalkyleneimine may be ahomopolymer containing only the same structure as the repeatingstructure represented by Formula 2, or may be a copolymer containing twoor more different structures as the repeating structure represented byFormula 2. A number average molecular weight of the polyalkyleneiminethat can be used to form the compound having the ammonium salt structureof the alkyl ester anion represented by Formula 1 can be, for example,equal to or greater than 200, and is preferably equal to or greater than300, and more preferably equal to or greater than 400. In addition, thenumber average molecular weight of the polyalkyleneimine can be, forexample, equal to or less than 10,000, and is preferably equal to orless than 5,000 and more preferably equal to or less than 2,000.

In the present invention and the present specification, the averagemolecular weight (weight-average molecular weight and number averagemolecular weight) is measured by gel permeation chromatography (GPC) andis a value obtained by performing standard polystyrene conversion.Unless otherwise noted, the average molecular weights shown in theexamples which will be described below are values(polystyrene-equivalent values) obtained by standard polystyreneconversion of the values measured under the following measurementconditions using GPC.

GPC device: HLC-8220 (manufactured by Tosoh Corporation)

Guard Column: TSK guard column Super HZM-H

Column: TSK gel Super HZ 2000, TSK gel Super HZ 4000, TSK gel Super HZ-M(manufactured by Tosoh Corporation, 4.6 mm (inner diameter)×15.0 cm,three kinds of columns are linked in series)

Eluent: Tetrahydrofuran (THF), including stabilizer(2,6-di-t-butyl-4-methylphenol)

Eluent flow rate: 0.35 mL/min

Column temperature: 40° C.

Inlet temperature: 40° C.

Refractive index (RI) measurement temperature: 40° C.

Sample concentration: 0.3% by mass

Sample injection amount: 10 μL

In addition, as the other embodiment of the nitrogen-containing polymer,polyallylamine can be used. The polyallylamine is a polymer ofallylamine and is a polymer having a plurality of repeating unitsrepresented by Formula 3.

The nitrogen atom N configuring an amino group of a side chain inFormula 3 can be converted to a nitrogen cation N⁺ to provide anammonium cation represented by Z⁺ in Formula 1. Then, an ammonium saltstructure can be formed with the alkyl ester anion, for example, asfollows.

A weight-average molecular weight of the polyallylamine that can be usedto form the compound having the ammonium salt structure of the alkylester anion represented by Formula 1 can be, for example, equal to orgreater than 200, and is preferably equal to or greater than 1,000, andmore preferably equal to or greater than 1,500. In addition, theweight-average molecular weight of the polyallylamine can be, forexample, equal to or less than 15,000, and is preferably equal to orless than 10,000 and more preferably equal to or less than 8,000.

The fact that the compound having a structure derived frompolyalkyleneimine or polyallylamine as the compound having the ammoniumsalt structure of the alkyl ester anion represented by Formula 1 isincluded in the back coating layer can be confirmed by analyzing thesurface of the back coating layer by a time-of-flight secondary ion massspectrometry (TOF-SIMS) or the like.

The compound having the ammonium salt structure of the alkyl ester anionrepresented by Formula 1 can be salt of a nitrogen-containing polymerand one or more fatty acids selected from the group consisting of fattyacids having 7 or more carbon atoms or fluorinated fatty acids having 7or more carbon atoms. The nitrogen-containing polymer forming salt canbe one kind or two or more kinds of nitrogen-containing polymers, andcan be, for example, a nitrogen-containing polymer selected from thegroup consisting of polyalkyleneimine or polyallylamine. The fatty acidsforming the salt can be one kind or two or more kinds of fatty acidsselected from the group consisting of fatty acids having 7 or morecarbon atoms or fluorinated fatty acids having 7 or more carbon atoms.The fluorinated fatty acid has a structure in which some or all of thehydrogen atoms configuring the alkyl group bonded to a carboxy groupCOOH in the fatty acid are substituted with fluorine atoms. For example,the salt forming reaction can easily proceed by mixing thenitrogen-containing polymer and the fatty acids described above at roomtemperature. The room temperature is, for example, approximately 20° C.to 25° C. In the one embodiment, one or more kinds ofnitrogen-containing polymers and one or more kinds of the fatty acidsdescribed above are used as components of the back coating layer formingcomposition, and the salt forming reaction can proceed by mixing thesein the step of preparing the back coating layer forming composition. Inthe one embodiment, one or more kinds of nitrogen-containing polymersand one or more kinds of the fatty acids described above are mixed toform a salt before preparing the back coating layer forming composition,and then, the back coating layer forming composition can be preparedusing this salt as a component of the back coating layer formingcomposition. In a case where the nitrogen-containing polymer and thefatty acid are mixed to form an ammonium salt of the alkyl ester anionrepresented by Formula 1, the nitrogen atom configuring thenitrogen-containing polymer and the carboxy group of the fatty acid maybe reacted to form the following structure, and a form including suchstructures are also included in the above compound.

Examples of the fatty acids include fatty acids having an alkyl groupdescribed above as R in Formula 1 and fluorinated fatty acids having afluorinated alkyl group described above as R in Formula 1.

A mixing ratio of the nitrogen-containing polymer and the fatty acidused to form the compound having the ammonium salt structure of thealkyl ester anion represented by Formula 1 is preferably 10:90 to 90:10,more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20,as a mass ratio of nitrogen-containing polymer:fatty acid. In addition,the used amount of the compound having the ammonium salt structure ofthe alkyl ester anion represented by Formula 1 can be, for example, 1.0to 20.0 parts by mass and is preferably 1.0 to 10.0 parts by mass withrespect to 100.0 parts by mass of carbon black, during preparation ofthe back coating layer forming composition. In addition, for example, ina case of preparing the back coating layer forming composition, 0.1 to10.0 parts by mass of the nitrogen-containing polymer can be used and0.5 to 8.0 parts by mass of the nitrogen-containing polymer ispreferably used with respect to 100.0 parts by mass of carbon black. Theused amount of the fatty acids described above can be, for example, 0.05to 10.0 parts by mass and is preferably 0.1 to 5.0 parts by mass, withrespect to 100.0 parts by mass of carbon black.

For the component contained in the back coating layer, the back coatinglayer can include a binding agent and can also include an additive. Inregards to the binding agent included in the back coating layer andadditives, a well-known technology regarding the back coating layer canbe applied, and a well-known technology regarding the list of themagnetic layer and/or the non-magnetic layer can also be applied. Forexample, for the back coating layer, descriptions disclosed inparagraphs 0018 to 0020 of JP2006-331625A and page 4, line 65, to page5, line 38, of U.S. Pat. No. 7,029,774B can be referred to.

Various Thicknesses

Regarding a thickness (total thickness) of the magnetic recordingmedium, an increase in recording capacity (high capacity) of themagnetic tape is required in accordance with a great increase ininformation content in recent years. Regarding a tape-shaped magneticrecording medium (that is, a magnetic tape), as a unit for increasingthe capacity, the thickness of the magnetic tape is decreased and alength of the magnetic tape accommodated in one roll of a magnetic tapecartridge is increased. From this point, the thickness (total thickness)of the magnetic tape is preferably 5.6 μm or less, more preferably 5.5μm or less, even more preferably 5.4 μm or less, still preferably 5.3 μmor less, and still more preferably 5.2 μm or less. In addition, from aviewpoint of ease of handling, the thickness of the magnetic tape ispreferably 3.0 μm or more and more preferably 3.5 μm or more.

The thickness (total thickness) of the magnetic tape can be measured bythe following method.

Ten samples (for example, 5 to 10 cm in length) are cut out from anyportion of the magnetic tape, and the samples are stacked to measure thethickness. A value (thickness per sample) obtained by calculating 1/10of the measured thickness is set as the total thickness. The thicknessmeasurement can be performed using a well-known measurement devicecapable of performing the thickness measurement at 0.1 μm order.

A thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of a magnetic head used, a head gaplength, a recording signal band, and the like, is normally 0.01 μm to0.15 μm, and is preferably 0.02 μm to 0.12 μm and more preferably 0.03μm to 0.1 μm, from a viewpoint of realization of high-density recording.The magnetic layer may be at least single layer, the magnetic layer maybe separated into two or more layers having different magneticproperties, and a configuration of a well-known multilayered magneticlayer can be applied. A thickness of the magnetic layer in a case wherethe magnetic layer is separated into two or more layers is the totalthickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm andis preferably 0.1 to 1.0 μm.

A thickness of the back coating layer is preferably 0.9 μm or less andmore preferably 0.1 to 0.7 μm.

Various thicknesses such as the thickness of the magnetic layer and thelike can be obtained by the following method.

A cross section of the magnetic tape in the thickness direction isexposed with an ion beam and the cross section observation of theexposed cross section is performed using a scanning electron microscopeor a transmission electron microscope. Various thicknesses can beobtained as the arithmetic mean of the thicknesses obtained at tworandom points in the cross section observation. Alternatively, variousthicknesses can be obtained as a designed thickness calculated under themanufacturing conditions.

Manufacturing Step Preparation of Each Layer Forming Composition

Composition for forming the magnetic layer, the non-magnetic layer, orthe back coating layer generally includes a solvent, together with thevarious components described above. As the solvent, one kind or two ormore kinds of various kinds of solvents usually used for producing acoating type magnetic recording medium can be used. The content of thesolvent in each layer forming composition is not particularly limited.For the solvent, a description disclosed in a paragraph 0153 ofJP2011-216149A can be referred to. A concentration of solid content anda solvent composition in each layer forming composition may be suitablyadjusted according to handleability of the composition, coatingconditions, and a thickness of each layer to be formed. A step ofpreparing a composition for forming the magnetic layer, the non-magneticlayer or the back coating layer can generally include at least akneading step, a dispersing step, and a mixing step provided before andafter these steps, in a case where necessary. Each step may be dividedinto two or more stages. Various components used in the preparation ofeach layer forming composition may be added at the beginning or duringany step. In addition, each component may be separately added in two ormore steps. For example, a binding agent may be separately added in akneading step, a dispersing step, and a mixing step for adjustingviscosity after the dispersion. In the manufacturing step of themagnetic tape, a well-known manufacturing technology of the related artcan be used as a part of step. In the kneading step, an open kneader, acontinuous kneader, a pressure kneader, or a kneader having a strongkneading force such as an extruder can be used. The details of thekneading step are disclosed in JP1989-106338A (JP-H01-106338A) andJP1989-79274A (JP-H01-79274A). As a disperser, various well-knowndispersers using a shear force such as a beads mill, a ball mill, a sandmill, or a homogenizer can be used. In the dispersion, the dispersionbeads can be preferably used. As dispersion beads, ceramic beads orglass beads are used and zirconia beads are preferable. A combination oftwo or more kinds of beads may be used. A bead diameter (particlediameter) and a beads filling percentage of the dispersion beads are notparticularly limited and may be set according to powder which is adispersion target. Each layer forming composition may be filtered by awell-known method before performing the coating step. The filtering canbe performed by using a filter, for example. As the filter used in thefiltering, a filter having a hole diameter of 0.01 to 3 μm (for example,filter made of glass fiber or filter made of polypropylene) can be used,for example.

Coating Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying the back coatinglayer forming composition onto the surface of the non-magnetic supportopposite to the surface provided with the non-magnetic layer and/or themagnetic layer (or non-magnetic layer and/or the magnetic layer is to beprovided). For details of the coating for forming each layer, adescription disclosed in a paragraph 0066 of JP2010-231843A can bereferred to.

Other Steps

For various other steps for manufacturing the magnetic tape, awell-known technology can be applied. For details of the various steps,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to, for example. For example, the coating layer of themagnetic layer forming composition can be subjected to an alignmentprocess in an alignment zone, while the coating layer is wet. For thealignment process, various well-known technologies disclosed in aparagraph 0052 of JP2010-24113A can be applied. For example, ahomeotropic alignment process can be performed by a well-known methodsuch as a method using a different polar facing magnet. In the alignmentzone, a drying speed of the coating layer can be controlled by atemperature and an air flow of the dry air and/or a transporting rate inthe alignment zone. In addition, the coating layer may be preliminarilydried before transporting to the alignment zone. As an example, themagnetic field strength in a homeotropic alignment process can be 0.1 to1.5 T.

Regarding the magnetic tape, a long magnetic tape raw material can beobtained through various steps. The obtained magnetic tape raw materialis cut (slit) by a well-known cutter to have a width of a magnetic tapeto be wound around the magnetic tape cartridge. The width is determinedaccording to the standard and is, for example, ½ inches. In the magnetictape obtained by slitting, a servo pattern can be formed. The formationof the servo pattern will be described later in detail.

Heat Treatment

In the one embodiment, the magnetic tape can be a magnetic tapemanufactured through the following heat treatment. In anotherembodiment, the magnetic tape can be manufactured without the followingheat treatment.

As the heat treatment, the magnetic tape slit and cut to have a widthdetermined according to the standard described above can be wound arounda core member and can be subjected to the heat treatment in the woundstate.

In the one embodiment, the heat treatment is performed in a state wherethe magnetic tape is wound around the core member for heat treatment(hereinafter, referred to as a “core for heat treatment”), the magnetictape after the heat treatment is wound around a cartridge reel of themagnetic tape cartridge, and a magnetic tape cartridge in which themagnetic tape is wound around the cartridge reel can be manufactured.

The core for heat treatment can be formed of metal, a resin, or paper.The material of the core for heat treatment is preferably a materialhaving high stiffness, from a viewpoint of preventing the occurrence ofa winding defect such as spoking or the like. From this viewpoint, thecore for heat treatment is preferably formed of metal or a resin. Inaddition, as an index for stiffness, a modulus of bending elasticity ofthe material for the core for heat treatment is preferably equal to orgreater than 0.2 GPa (gigapascal) and more preferably equal to orgreater than 0.3 GPa. Meanwhile, since the material having highstiffness is normally expensive, the use of the core for heat treatmentof the material having stiffness exceeding the stiffness capable ofpreventing the occurrence of the winding defect causes the costincrease. By considering the viewpoint described above, the modulus ofbending elasticity of the material for the core for heat treatment ispreferably equal to or smaller than 250 GPa. The modulus of bendingelasticity is a value measured based on international organization forstandardization (ISO) 178 and the modulus of bending elasticity ofvarious materials is well known. In addition, the core for heattreatment can be a solid or hollow core member. In a case of a hollowshape, a wall thickness is preferably equal to or greater than 2 mm,from a viewpoint of maintaining the stiffness. In addition, the core forheat treatment may include or may not include a flange.

The magnetic tape having a length equal to or greater than a length tobe finally accommodated in the magnetic tape cartridge (hereinafter,referred to as a “final product length”) is prepared as the magnetictape wound around the core for heat treatment, and it is preferable toperform the heat treatment by placing the magnetic tape in the heattreatment environment, in a state where the magnetic tape is woundaround the core for heat treatment. The magnetic tape length woundaround the core for heat treatment is equal to or greater than the finalproduct length, and is preferably the “final product length +α”, from aviewpoint of ease of winding around the core for heat treatment. This ais preferably equal to or greater than 5 m, from a viewpoint of ease ofthe winding. The tension in a case of winding around the core for heattreatment is preferably equal to or greater than 0.1 N (newton). Inaddition, from a viewpoint of preventing the occurrence of excessivedeformation during the manufacturing, the tension in a case of windingaround the core for heat treatment is preferably equal to or smallerthan 1.5 N and more preferably equal to or smaller than 1.0 N. An outerdiameter of the core for heat treatment is preferably equal to orgreater than 20 mm and more preferably equal to or greater than 40 mm,from viewpoints of ease of the winding and preventing coiling (curl inlongitudinal direction). The outer diameter of the core for heattreatment is preferably equal to or smaller than 100 mm and morepreferably equal to or smaller than 90 mm. A width of the core for heattreatment may be equal to or greater than the width of the magnetic tapewound around this core. In addition, after the heat treatment, in a caseof detaching the magnetic tape from the core for heat treatment, it ispreferable that the magnetic tape and the core for heat treatment aresufficiently cooled and magnetic tape is detached from the core for heattreatment, in order to prevent the occurrence of the tape deformationwhich is not intended during the detaching operation. It is preferablethe detached magnetic tape is wound around another core temporarily(referred to as a “core for temporary winding”), and the magnetic tapeis wound around a cartridge reel (generally, outer diameter isapproximately 40 to 50 mm) of the magnetic tape cartridge from the corefor temporary winding. Accordingly, a relationship between the insideand the outside with respect to the core for heat treatment of themagnetic tape in a case of the heat treatment can be maintained and themagnetic tape can be wound around the cartridge reel of the magnetictape cartridge. Regarding the details of the core for temporary windingand the tension in a case of winding the magnetic tape around the core,the description described above regarding the core for heat treatmentcan be referred to. In an embodiment in which the heat treatment issubjected to the magnetic tape having a length of the “final productlength +α”, the length corresponding to “+α” may be cut in any stage.For example, in one embodiment, the magnetic tape having the finalproduct length may be wound around the cartridge reel of the magnetictape cartridge from the core for temporary winding and the remaininglength corresponding the “+α” may be cut. From a viewpoint of decreasingthe amount of the portion to be cut out and removed, the a is preferablyequal to or smaller than 20 m.

The specific embodiment of the heat treatment performed in a state ofbeing wound around the core member as described above is describedbelow.

An atmosphere temperature for performing the heat treatment(hereinafter, referred to as a “heat treatment temperature”) ispreferably equal to or higher than 40° C. and more preferably equal toor higher than 50° C. On the other hand, from a viewpoint of preventingthe excessive deformation, the heat treatment temperature is preferablyequal to or lower than 75° C., more preferably equal to or lower than70° C., and even more preferably equal to or lower than 65° C.

A weight absolute humidity of the atmosphere for performing the heattreatment is preferably equal to or greater than 0.1 g/kg Dry air andmore preferably equal to or greater than 1 g/kg Dry air. The atmospherein which the weight absolute humidity is in the range described above ispreferable, because it can be prepared without using a special devicefor decreasing moisture. On the other hand, the weight absolute humidityis preferably equal to or smaller than 70 g/kg Dry air and morepreferably equal to or smaller than 66 g/kg Dry air, from a viewpoint ofpreventing a deterioration in workability by dew condensation. The heattreatment time is preferably equal to or longer than 0.3 hours and morepreferably equal to or longer than 0.5 hours. In addition, the heattreatment time is preferably equal to or shorter than 48 hours, from aviewpoint of production efficiency.

Regarding the control of the curvature of the magnetic tape in thelongitudinal direction, as any value of the heat treatment temperature,heat treatment time, modulus of bending elasticity of a core for theheat treatment, and tension at the time of winding around the core forthe heat treatment is large, the value of the curvature tends to furtherdecrease.

Formation of Servo Pattern

A servo pattern can also be formed on the magnetic tape by a well-knownmethod, in order to realize tracking control of a magnetic head of amagnetic recording and reproducing device and control of a running speedof the magnetic tape. The “formation of the servo pattern” can be“recording of a servo signal”. The dimension information of the magnetictape in the width direction during the running can be obtained using aservo signal, and the dimension of the magnetic tape in the widthdirection can be controlled by adjusting and changing the tensionapplied in the longitudinal direction of the magnetic tape according tothe obtained dimension information.

The formation of the servo pattern will be described below.

The servo pattern is generally formed along a longitudinal direction ofthe magnetic tape. As a system of control using a servo signal (servocontrol), timing-based servo (TBS), amplitude servo, or frequency servois used.

As shown in European Computer Manufacturers Association (ECMA)-319 (June2001), a timing-based servo system is used in a magnetic tape based on alinear-tape-open (LTO) specification (generally referred to as an “LTOtape”). In this timing-based servo system, the servo pattern isconfigured by continuously disposing a plurality of pairs of magneticstripes (also referred to as “servo stripes”) not parallel to each otherin a longitudinal direction of the magnetic tape. The servo system is asystem of performing head tracking using a servo signal. In theinvention and the specification, the “timing-based servo pattern” refersto a servo pattern that enables head tracking in a servo system of atiming-based servo system. As described above, a reason for that theservo pattern is configured with one pair of magnetic stripes notparallel to each other is because a servo signal reading element passingon the servo pattern recognizes a passage position thereof.Specifically, one pair of the magnetic stripes are formed so that a gapthereof is continuously changed along the width direction of themagnetic tape, and a relative position of the servo pattern and theservo signal reading element can be recognized, by the reading of thegap thereof by the servo signal reading element. The information of thisrelative position can realize the tracking of a data track. Accordingly,a plurality of servo tracks are generally set on the servo pattern alongthe width direction of the magnetic tape.

The servo band is configured of servo patterns continuous in thelongitudinal direction of the magnetic tape. A plurality of servo bandsare normally provided on the magnetic tape. For example, the numberthereof is 5 in the LTO tape. A region interposed between two adjacentservo bands is a data band. The data band is configured of a pluralityof data tracks and each data track corresponds to each servo track.

In one embodiment, as shown in JP2004-318983A, information showing thenumber of servo band (also referred to as “servo band identification(ID)” or “Unique Data Band Identification Method (UDIM) information”) isembedded in each servo band. This servo band ID is recorded by shiftinga specific servo stripe among the plurality of pair of servo stripes inthe servo band so that the position thereof is relatively displaced inthe longitudinal direction of the magnetic tape. Specifically, theposition of the shifted specific servo stripe among the plurality ofpairs of servo stripes is changed for each servo band. Accordingly, therecorded servo band ID becomes unique for each servo band, andtherefore, the servo band can be uniquely specified by only reading oneservo band by the servo signal reading element.

In a method of uniquely specifying the servo band, a staggered method asshown in ECMA-319 (June 2001) is used. In this staggered method, aplurality of the groups of one pair of magnetic stripes (servo stripe)not parallel to each other which are continuously disposed in thelongitudinal direction of the magnetic tape is recorded so as to beshifted in the longitudinal direction of the magnetic tape for eachservo band. A combination of this shifted servo band between theadjacent servo bands is set to be unique in the entire magnetic tape,and accordingly, the servo band can also be uniquely specified byreading of the servo pattern by two servo signal reading elements.

In addition, as shown in ECMA-319 (June 2001), information showing theposition in the longitudinal direction of the magnetic tape (alsoreferred to as “Longitudinal Position (LPOS) information”) is normallyembedded in each servo band. This LPOS information is recorded so thatthe position of one pair of servo stripes is shifted in the longitudinaldirection of the magnetic tape, in the same manner as the UDIMinformation. However, unlike the UDIM information, the same signal isrecorded on each servo band in this LPOS information.

Other information different from the UDIM information and the LPOSinformation can be embedded in the servo band. In this case, theembedded information may be different for each servo band as the UDIMinformation, or may be common in all of the servo bands, as the LPOSinformation.

In addition, as a method of embedding the information in the servo band,a method other than the method described above can be used. For example,a predetermined code may be recorded by thinning out a predeterminedpair among the group of pairs of the servo stripes.

A servo pattern forming head is also referred to as a servo write head.The servo write head generally includes pairs of gaps corresponding tothe pairs of magnetic stripes by the number of servo bands. In general,a core and a coil are respectively connected to each of the pairs ofgaps, and a magnetic field generated in the core can generate leakagemagnetic field in the pairs of gaps, by supplying a current pulse to thecoil. In a case of forming the servo pattern, by inputting a currentpulse while causing the magnetic tape to run on the servo write head,the magnetic pattern corresponding to the pair of gaps is transferred tothe magnetic tape, and the servo pattern can be formed. A width of eachgap can be suitably set in accordance with a density of the servopattern to be formed. The width of each gap can be set as, for example,equal to or smaller than 1 μm, 1 to 10 μm, or equal to or greater than10 μm.

Before forming the servo pattern on the magnetic tape, a demagnetization(erasing) process is generally performed on the magnetic tape. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape by using a DC magnet and an AC magnet. The erasingprocess includes direct current (DC) erasing and alternating current(AC) erasing. The AC erasing is performed by slowing decreasing anintensity of the magnetic field, while reversing a direction of themagnetic field applied to the magnetic tape. Meanwhile, the DC erasingis performed by applying the magnetic field in one direction to themagnetic tape. The DC erasing further includes two methods. A firstmethod is horizontal DC erasing of applying the magnetic field in onedirection along a longitudinal direction of the magnetic tape. A secondmethod is vertical DC erasing of applying the magnetic field in onedirection along a thickness direction of the magnetic tape. The erasingprocess may be performed with respect to all of the magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field to the servo pattern to be formed isdetermined in accordance with the direction of erasing. For example, ina case where the horizontal DC erasing is performed to the magnetictape, the formation of the servo pattern is performed so that thedirection of the magnetic field and the direction of erasing is oppositeto each other. Accordingly, the output of the servo signal obtained bythe reading of the servo pattern can be increased. As disclosed inJP2012-53940A, in a case where the magnetic pattern is transferred tothe magnetic tape subjected to the vertical DC erasing by using the gap,the servo signal obtained by the reading of the formed servo pattern hasa unipolar pulse shape. Meanwhile, in a case where the magnetic patternis transferred to the magnetic tape subjected to the horizontal DCerasing by using the gap, the servo signal obtained by the reading ofthe formed servo pattern has a bipolar pulse shape.

Usually, after the formation of the servo pattern, the magnetic tape iswound around the core of the magnetic tape container and accommodated inthe magnetic tape container. As described above, the magnetic tapecontainer is a magnetic tape cartridge in one aspect and a magneticrecording and reproducing device including a magnetic head in the otheraspect.

Magnetic Head

In the invention and the specification, the “magnetic recording andreproducing device” means a device capable of performing at least one ofthe recording of data on the magnetic tape or the reproducing of datarecorded on the magnetic tape. Such a device is generally called a driveand can be a tape drive for recording digital data. The magnetic tapecontainer can be a magnetic tape cartridge in one aspect, and can be amagnetic recording and reproducing device including a magnetic head inthe other aspect. The magnetic tape cartridge can be inserted into themagnetic recording and reproducing device, and the magnetic tape can berun in the magnetic recording and reproducing device to record data onthe magnetic tape and/or reproduce the recorded data by the magnetichead. The magnetic head included in the magnetic recording andreproducing device can be a recording head capable of performing therecording of data on the magnetic tape, and can also be a reproducinghead capable of performing the reproducing of data recorded on themagnetic tape. In addition, in the embodiment, the magnetic recordingand reproducing device can include both of a recording head and areproducing head as separate magnetic heads. In another embodiment, themagnetic head included in the magnetic recording and reproducing devicemay have a configuration in which both the recording element and thereproducing element are comprised in one magnetic head. As thereproducing head, a magnetic head (MR head) including a magnetoresistive(MR) element capable of reading information recorded on the magnetictape with excellent sensitivity as the reproducing element ispreferable. As the MR head, various well-known MR heads (for example, aGiant Magnetoresistive (GMR) head, or a Tunnel Magnetoresistive (TMR)head) can be used. In addition, the magnetic head which performs therecording of data and/or the reproducing of data may include a servopattern reading element. Alternatively, as a head other than themagnetic head which performs the recording of data and/or thereproducing of data, a magnetic head (servo head) including a servopattern reading element may be included in the magnetic recording andreproducing device. For example, the magnetic head which performs therecording of data and/or reproducing of the recorded data (hereinafter,also referred to as a “recording and reproducing head”) can include twoservo signal reading elements, and each of the two servo signal readingelements can read two adjacent servo bands with the data band interposedtherebetween at the same time. One or a plurality of elements for datacan be disposed between the two servo signal reading elements. Theelement for recording data (recording element) and the element forreproducing data (reproducing element) are collectively referred to as“elements for data”.

By reproducing data using the reproducing element having a narrowreproducing element width as the reproducing element, the data recordedat high density can be reproduced with high sensitivity. From thisviewpoint, the reproducing element width of the reproducing element ispreferably 0.8 μm or less. The reproducing element width of thereproducing element can be, for example, 0.1 μm or more. However, it isalso preferable to fall below this value from the above viewpoint.

On the other hand, as the reproducing element width decreases, aphenomenon such as reproducing failure due to off-track is more likelyto occur. In order to suppress the occurrence of such a phenomenon, itis preferable to use a magnetic recording and reproducing device thatcontrols the dimension of the magnetic tape in the width direction byadjusting and changing the tension applied in the longitudinal directionof the magnetic tape during the running.

Here, the “reproducing element width” refers to a physical dimension ofthe reproducing element width. Such physical dimensions can be measuredwith an optical microscope, a scanning electron microscope, or the like.

In a case of recording data and/or reproducing recorded data, first,head tracking can be performed using a servo signal. That is, as theservo signal reading element follows a predetermined servo track, theelement for data can be controlled to pass on the target data track. Themovement of the data track is performed by changing the servo track tobe read by the servo signal reading element in the tape width direction.

In addition, the recording and reproducing head can perform therecording and/or reproducing with respect to other data bands. In thiscase, the servo signal reading element is moved to a predetermined servoband by using the UDIM information described above, and the trackingwith respect to the servo band may be started.

FIG. 8 shows an example of disposition of data bands and servo bands. InFIG. 8, a plurality of servo bands 1 are disposed to be interposedbetween guide bands 3 in a magnetic layer of a magnetic tape T. Aplurality of regions 2 each of which is interposed between two servobands are data bands. The servo pattern is a magnetized region and isformed by magnetizing a specific region of the magnetic layer by a servowrite head. The region magnetized by the servo write head (positionwhere a servo pattern is formed) is determined by standards. Forexample, in an LTO Ultrium format tape which is based on a localstandard, a plurality of servo patterns tilted in a tape width directionas shown in FIG. 9 are formed on a servo band, in a case ofmanufacturing a magnetic tape. Specifically, in FIG. 9, a servo frame SFon the servo band 1 is configured with a servo sub-frame 1 (SSF1) and aservo sub-frame 2 (SSF2). The servo sub-frame 1 is configured with an Aburst (in FIG. 9, reference numeral A) and a B burst (in FIG. 9,reference numeral B). The A burst is configured with servo patterns A1to A5 and the B burst is configured with servo patterns B1 to B5.Meanwhile, the servo sub-frame 2 is configured with a C burst (in FIG.9, reference numeral C) and a D burst (in FIG. 9, reference numeral D).The C burst is configured with servo patterns C1 to C4 and the D burstis configured with servo patterns D1 to D4. Such 18 servo patterns aredisposed in the sub-frames in the arrangement of 5, 5, 4, 4, as the setsof 5 servo patterns and 4 servo patterns, and are used for identifyingthe servo frames. FIG. 9 shows one servo frame for explaining. However,in practice, in the magnetic layer of the magnetic tape in which thehead tracking servo in the timing-based servo system is performed, aplurality of servo frames are disposed in each servo band in a runningdirection. In FIG. 9, an arrow shows the running direction. For example,an LTO Ultrium format tape generally includes 5,000 or more servo framesper a tape length of 1 m, in each servo band of the magnetic layer.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to embodiments shown in theexamples. “Parts” and “%” in the following description mean “parts bymass” and “% by mass”, unless otherwise noted. In addition, steps andevaluations described below are performed in an environment of anatmosphere temperature of 23° C.±1° C., unless otherwise noted. Further,“eq” described below indicates an equivalent which is a unit whichcannot be converted into the SI unit system.

Non-Magnetic Support

In Table 1, “PET” in the column of the non-magnetic support indicates apolyethylene terephthalate support and “PEN” indicates a polyethylenenaphthalate support.

Ferromagnetic Powder

In Table 1, “BaFe” in a column of the type of the ferromagnetic powderis a hexagonal barium ferrite powder having an average particle size(average plate diameter) of 21 nm.

In Table 1, “SrFe1” of the column of the type of ferromagnetic powderindicates a hexagonal strontium ferrite powder produced as follows.

1,707 g of SrCO₃, 687 g of H₃BO₃, 1,120 g of Fe₂O₃, 45 g of Al(OH)₃, 24g of BaCO₃, 13 g of CaCO₃, and 235 g of Nd₂O₃ were weighed and mixed ina mixer to obtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,390° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the prepared amorphous body was put into an electronic furnace,heated to 635° C. (crystallization temperature) at a rate of temperaturerise of 3.5° C./min, and held at the same temperature for 5 hours, andhexagonal strontium ferrite particles were precipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1,000 g of zirconia beads having a particle diameter of 1 mm,and 800 mL of an acetic acid aqueous solution having a concentration of1% were added to a glass bottle, and a dispersion process was performedin a paint shaker for 3 hours. After that, the obtained dispersionliquid and the beads were separated and put in a stainless still beaker.The dispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 18 nm, an activation volume was 902nm³, an anisotropy constant Ku was 2.2×10⁵ J/m³, and a massmagnetization σs was 49 A×m²/kg.

12 mg of a sample powder was collected from the hexagonal strontiumferrite powder obtained as described above, the element analysis of afiltrate obtained by the partial dissolving of this sample powder underthe dissolving conditions described above was performed by the ICPanalysis device, and a surface layer portion content of a neodymium atomwas obtained.

Separately, 12 mg of a sample powder was collected from the hexagonalstrontium ferrite powder obtained as described above, the elementanalysis of a filtrate obtained by the total dissolving of this samplepowder under the dissolving conditions described above was performed bythe ICP analysis device, and a bulk content of a neodymium atom wasobtained.

The content (bulk content) of the neodymium atom in the hexagonalstrontium ferrite powder obtained as described above with respect to 100atom % of iron atom was 2.9 atom %. In addition, the surface layerportion content of the neodymium atom was 8.0 atom %. A ratio of thesurface layer portion content and the bulk content, “surface layerportion content/bulk content” was 2.8 and it was confirmed that theneodymium atom is unevenly distributed on the surface layer of theparticles.

A crystal structure of the hexagonal ferrite shown by the powderobtained as described above was confirmed by scanning CuKα ray under theconditions of a voltage of 45 kV and intensity of 40 mA and measuring anX-ray diffraction pattern under the following conditions (X-raydiffraction analysis). The powder obtained as described above showed acrystal structure of magnetoplumbite type (M type) hexagonal ferrite. Inaddition, a crystal phase detected by the X-ray diffraction analysis wasa magnetoplumbite type single phase.

PANalytical X'Pert Pro diffractometer, PIXcel detector

Soller slit of incident beam and diffraction beam: 0.017 radians

Fixed angle of dispersion slit: ¼ degrees

Mask: 10 mm

Scattering prevention slit: ¼ degrees

Measurement mode: continuous

Measurement time per 1 stage: 3 seconds

Measurement speed: 0.017 degrees per second

Measurement step: 0.05 degree

In Table 1, “SrFe2” of the column of the type of ferromagnetic powderindicates a hexagonal strontium ferrite powder produced as follows.

1,725 g of SrCO₃, 666 g of H₃BO₃, 1,332 g of Fe₂O₃, 52 g of Al(OH)₃, 34g of CaCO₃, and 141 g of BaCO₃ were weighed and mixed in a mixer toobtain a raw material mixture.

The obtained raw material mixture was dissolved in a platinum crucibleat a melting temperature of 1,380° C., and a tap hole provided on thebottom of the platinum crucible was heated while stirring the melt, andthe melt was tapped in a rod shape at approximately 6 g/sec. The tapliquid was rolled and cooled with a water cooling twin roller to preparean amorphous body.

280 g of the obtained amorphous body was put into an electronic furnace,heated to 645° C. (crystallization temperature), and held at the sametemperature for 5 hours, and hexagonal strontium ferrite particles wereprecipitated (crystallized).

Then, the crystallized material obtained as described above includingthe hexagonal strontium ferrite particles was coarse-pulverized with amortar, 1,000 g of zirconia beads having a particle diameter of 1 mm,and 800 mL of an acetic acid aqueous solution having a concentration of1% were added to a glass bottle, and a dispersion process was performedin a paint shaker for 3 hours. After that, the obtained dispersionliquid and the beads were separated and put in a stainless still beaker.The dispersion liquid was left at a liquid temperature of 100° C. for 3hours, subjected to a dissolving process of a glass component,precipitated with a centrifugal separator, decantation was repeated forcleaning, and drying was performed in a heating furnace at a furnaceinner temperature of 110° C. for 6 hours, to obtain hexagonal strontiumferrite powder.

Regarding the hexagonal strontium ferrite powder obtained as describedabove, an average particle size was 19 nm, an activation volume was1,102 nm³, an anisotropy constant Ku was 2.0×10⁵ J/m³, and a massmagnetization σs was 50 A×m²/kg.

In Table 1, “ε-iron oxide” of the column of the type of ferromagneticpowder indicates a ε-iron oxide powder produced as follows.

4.0 g of ammonia aqueous solution having a concentration of 25% wasadded to a material obtained by dissolving 8.3 g of iron (III) nitratenonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg ofcobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and1.5 g of polyvinyl pyrrolidone (PVP) in 90 g of pure water, whilestirring by using a magnetic stirrer, in an atmosphere under theconditions of an atmosphere temperature of 25° C., and the mixture wasstirred for 2 hours still under the temperature condition of theatmosphere temperature of 25° C. A citric acid solution obtained bydissolving 1 g of citric acid in 9 g of pure water was added to theobtained solution and stirred for 1 hour. The powder precipitated afterthe stirring was collected by centrifugal separation, washed with purewater, and dried in a heating furnace at a furnace inner temperature of80° C.

800 g of pure water was added to the dried powder and the powder wasdispersed in water again, to obtain a dispersion liquid. The obtaineddispersion liquid was heated to a liquid temperature of 50° C., and 40 gof ammonia aqueous solution having a concentration of 25% was addeddropwise while stirring. The stirring was performed for 1 hour whileholding the temperature of 50° C., and 14 mL of tetraethoxysilane (TEOS)was added dropwise and stirred for 24 hours. 50 g of ammonium sulfatewas added to the obtained reaction solution, the precipitated powder wascollected by centrifugal separation, washed with pure water, and driedin a heating furnace at a furnace inner temperature of 80° C. for 24hours, and a precursor of ferromagnetic powder was obtained.

The heating furnace at a furnace inner temperature of 1,000° C. wasfilled with the obtained precursor of ferromagnetic powder in theatmosphere and subjected to heat treatment for 4 hours.

The heat-treated precursor of ferromagnetic powder was put into sodiumhydroxide (NaOH) aqueous solution having a concentration of 4 mol/L, theliquid temperature was held at 70° C., stirring was performed for 24hours, and accordingly, a silicon acid compound which was an impuritywas removed from the heat-treated precursor of ferromagnetic powder.

After that, by the centrifugal separation process, ferromagnetic powderobtained by removing the silicon acid compound was collected and washedwith pure water, and ferromagnetic powder was obtained.

The composition of the obtained ferromagnetic powder was confirmed byInductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), andGa, Co, and Ti substitution type ε-iron oxide(ε-Ga_(0.28)Co_(0.05)Ti_(0.05)Fe_(1.62)O₃) was obtained. In addition,the X-ray diffraction analysis was performed under the same conditionsas the conditions described regarding the hexagonal strontium ferritepowder SrFe1 in advance, and it was confirmed that the obtainedferromagnetic powder has a crystal structure of a single phase which isan ε phase not including a crystal structure of an α phase and a γ phase(ε-iron oxide type crystal structure) from the peak of the X-raydiffraction pattern.

Regarding the obtained (ε-iron oxide powder, an average particle sizewas 12 nm, an activation volume was 746 nm³, an anisotropy constant Kuwas 1.2×10⁵ J/m³, and a mass magnetization σs was 16 A×m²/kg.

The activation volume and the anisotropy constant Ku of the hexagonalstrontium ferrite powder and the ε-iron oxide powder are values obtainedby the method described above regarding each ferromagnetic powder byusing an oscillation sample type magnetic-flux meter (manufactured byToei Industry Co., Ltd.).

In addition, the mass magnetization σs is a value measured at themagnetic field strength of 1,194 kA/m (15 kOe) by using an oscillationsample type magnetic-flux meter (manufactured by Toei Industry Co.,Ltd.).

Example 1 (1) List of Magnetic Layer Forming Composition

Magnetic Liquid

Ferromagnetic powder (see Table 1): 100.0 parts

SO₃Na group-containing polyurethane resin: 14.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.4 meq/g

Cyclohexanone: 150 parts

Methyl ethyl ketone: 150 parts

Abrasive Solution A

Alumina abrasive (average particle size: 100 nm): 3.0 parts

Sulfonic acid group-containing polyurethane resin: 0.3 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.3 meq/g

Cyclohexanone: 26.7 parts

Abrasive Solution B

Diamond abrasive (average particle size: 100 nm): 1.0 part

Sulfonic acid group-containing polyurethane resin: 0.1 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.3 meq/g

Cyclohexanone: 26.7 parts

Silica Sol

Colloidal silica (average particle size: 100 nm): 0.2 part

Methyl ethyl ketone: 1.4 parts

Other Components

Stearic acid: 2.0 parts

Butyl stearate: 10.0 parts

Polyisocyanate (CORONATE manufactured by Nippon Polyurethane IndustryCo., Ltd.): 2.5 parts

Cyclohexanone: 200.0 parts

Methyl ethyl ketone: 200.0 parts

(2) List of Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder (α-iron oxide): 100.0 parts

Average particle size (average major axis length): 10 nm

Average acicular ratio: 1.9

Brunauer-emmett-teller (BET) specific surface area: 75 m²/g

Carbon black: 25.0 parts

Average particle size: 20 nm

SO₃Na group-containing polyurethane resin: 18.0 parts

Weight-average molecular weight: 70,000, SO₃Na group: 0.2 meq/g

Stearic acid: 1.0 part

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

(3) List of Back Coating Layer Forming Composition

Carbon black: 100.0 parts

BP-800 manufactured by Cabot Corporation, average particle size: 17 nm

SO₃Na group-containing polyurethane resin (SO₃Na group: 70 eq/ton): 20.0parts

OSO₃K group-containing vinyl chloride resin (OSO₃K group: 70 eq/ton):30.0 parts

Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., numberaverage molecular weight: 600): See Table 1

Stearic acid: see Table 1

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: 2.0 parts

Stearic acid amide: 0.1 parts

(4) Manufacturing of Magnetic Tape and Magnetic Tape Cartridge

A magnetic liquid was prepared by dispersing the components of themagnetic liquid with a batch type vertical sand mill for 24 hours. Asdispersion beads, zirconia beads having a bead diameter of 0.5 mm wereused.

Regarding the abrasive solution, the above components of the abrasivesolution A and the abrasive solution B were dispersed for 24 hours witha batch type ultrasonic device (20 kHz, 300 W), respectively, to obtainthe abrasive solution A and the abrasive solution B.

The magnetic liquid, the abrasive solution A and the abrasive solution Bwere mixed with the above silica sol and other components, and thendispersed in a batch type ultrasonic device (20 kHz, 300 W) for 30minutes. After that, the obtained mixed solution was filtered by using afilter having a hole diameter of 0.5 μm, and the magnetic layer formingcomposition was prepared.

For the non-magnetic layer forming composition, the components weredispersed by using a batch type vertical sand mill for 24 hours. Asdispersion beads, zirconia beads having a bead diameter of 0.1 mm wereused. The obtained dispersion liquid was filtered with a filter having ahole diameter of 0.5 μm, and a non-magnetic layer forming compositionwas prepared.

Regarding the back coating layer forming composition, the abovecomponents were kneaded with a continuous kneader and then dispersedusing a sand mill. After adding 40.0 parts of polyisocyanate (Coronate Lmanufactured by Nippon Polyurethane Industry Co., Ltd.) and 1000.0 partsof methyl ethyl ketone to the obtained dispersion liquid, the mixturewas filtered using a filter having a hole diameter of 1 μm to prepare aback coating layer forming composition.

The non-magnetic layer forming composition prepared in the section wasapplied to a surface of a support which is a type shown in Table 1having a thickness of 4.1 μm so that the thickness after the dryingbecomes 0.7 μm and was dried to form a non-magnetic layer.

Then, the magnetic layer forming composition prepared as described abovewas applied onto the non-magnetic layer so that the thickness after thedrying is 0.1 μm, and a coating layer was formed.

After that, a homeotropic alignment process was performed by applying amagnetic field having a magnetic field strength of 0.3 T in a verticaldirection with respect to a surface of a coating layer, while thecoating layer of the magnetic layer forming composition is wet. Then,the drying was performed to form the magnetic layer.

After that, the back coating layer forming composition prepared asdescribed above was applied to the surface of the support made ofpolyethylene naphthalate on a side opposite to the surface where thenon-magnetic layer and the magnetic layer were formed, so that thethickness after the drying becomes 0.3 μm, and was dried to form a backcoating layer.

After that, a surface smoothing treatment (calender process) wasperformed by using a calender roll configured of only a metal roll, at aspeed of 100 m/min, linear pressure of 300 kg/cm), and a calendertemperature (surface temperature of a calender roll) of 90° C. By doingso, a long magnetic tape raw material was obtained.

Then, after the heat treatment for 36 hours in an environment of anatmosphere temperature of 70° C., a long magnetic tape raw material wasslit into a ½ inches width to obtain a magnetic tape. By recording aservo signal on the magnetic layer of the obtained magnetic tape with acommercially available servo writer, a magnetic tape having a servopattern (timing-based servo pattern) was obtained in an arrangementaccording to the LTO (Linear Tape-Open) Ultrium format. By recording aservo signal on a magnetic layer of the obtained magnetic tape with acommercially available servo writer, the magnetic tape including a databand, a servo band, and a guide band in the disposition according to alinear-tape-open (LTO) Ultrium format, and including a servo pattern(timing-based servo pattern) having the disposition and shape accordingto the LTO Ultrium format on the servo band was obtained. The servopattern formed by doing so is a servo pattern disclosed in JapaneseIndustrial Standards (JIS) X6175:2006 and Standard ECMA-319 (June 2001).

The magnetic tape (length of 960 m) after the servo signal recording waswound around the core for heat treatment, and the heat treatment wasperformed in a state of being wound around this core. As the core forheat treatment, a solid core member (outer diameter: 50 mm) formed of aresin and having a value of a modulus of bending elasticity shown inTable 1 was used, and the tension in a case of the winding was set as avalue shown in Table 1. The heat treatment temperature and heattreatment time in the heat treatment were set to values shown inTable 1. The weight absolute humidity in the atmosphere in which theheat treatment was performed was 10 g/kg Dry air.

After the heat treatment, the magnetic tape and the core for heattreatment were sufficiently cooled, the magnetic tape was detached fromthe core for heat treatment and wound around the core for temporarywinding, and then, the magnetic tape having the final product length(950 m) was wound around the reel of the magnetic tape cartridge fromthe core for temporary winding. The remaining length of 10 m was cut outand the leader tape based on section 9 of Standard European ComputerManufacturers Association (ECMA)-319 (June 2001) Section 3 was bonded tothe terminal of the cut side by using a commercially available splicingtape. As the core for temporary winding, a solid core member having thesame outer diameter and formed of the same material as the core for heattreatment was used, and the tension in a case of winding was set as 0.6N.

As the magnetic tape cartridge accommodating the magnetic tape describedabove, a single reel type magnetic tape cartridge having theconfiguration shown in FIG. 1 was used. The reel hub of this magnetictape cartridge is a single-layer structure reel hub (thickness: 2.5 mm,outer diameter: 44 mm) obtained by injection molding glass fiberreinforced polycarbonate. The magnetic tape was wound around the reelhub of the magnetic tape cartridge while applying a tension of 1.0 N orless in the longitudinal direction of the tape, and the magnetic tapewas housed in the magnetic tape cartridge.

As described above, a single reel type magnetic tape cartridge ofExample 1 in which a magnetic tape having a length of 950 m was woundaround a reel was manufactured.

It can be confirmed by the following method that the back coating layerof the magnetic tape contains a compound formed of polyethyleneimine andstearic acid and having an ammonium salt structure of an alkyl esteranion represented by Formula 1.

A sample is cut out from a magnetic tape, and X-ray photoelectronspectroscopy analysis is performed on the surface of the back coatinglayer (measurement area: 300 μm×700 μm) using an ESCA device.Specifically, wide scan measurement is performed by the ESCA deviceunder the following measurement conditions. In the measurement results,peaks are confirmed at a position of a binding energy of the ester anionand a position of a binding energy of the ammonium cation.

Device: AXIS-ULTRA manufactured by Shimadzu Corporation

Excited X-ray source: Monochromatic Al-Kα ray

Scan range: 0 to 1,200 eV

Path energy: 160 eV

Energy resolution: 1 eV/step

Capturing Time: 100 ms/step

Number of times of integration: 5

In addition, a sample piece having a length of 3 cm is cut out from themagnetic tape, and attenuated total reflection-fouriertransform-infrared spectrometer (ATR-FT-IR) measurement (reflectionmethod) is performed on the surface of the back coating layer, and, inthe measurement result, the absorption is confirmed on a wave numbercorresponding to absorption of COO⁻(1,540 cm⁻¹ or 1,430 cm⁻¹) and a wavenumber corresponding to the absorption of the ammonium cation (2,400cm⁻¹).

The above steps were repeated to manufacture three magnetic tapecartridges, one magnetic tape cartridge was used for the following (5),another magnetic tape cartridge was used for the following (9), andstill another magnetic tape cartridge was used for the magnetic tapeextracted from the magnetic tape cartridge as in following (6) to (8).

(5) Measurement of Reference Circle Center Position Deviation

In regard to the trajectory of one rotation drawn by the magnetic tapein a case of drawing the magnetic tape wound around the reel (core) ofthe magnetic tape cartridge from the core by the method described above,the maximum value of the deviation of the center position of the averageminimum region reference circle (reference circle center positiondeviation) of the trajectory of one rotation was obtained for the threepoints of the magnetic tape in the width direction, by using LK-G85 andLK-GD500 manufactured by KEYENCE as the laser displacement meter andCZ-H35S and CZ-C21A manufactured by KEYENCE as the opticaldiscrimination sensor. The measurement was carried out by extracting thereel around which the magnetic tape was wound from the case of themagnetic tape cartridge and transferring the reel to the cartridge casehaving the opening portion as described above.

(6) Number of Recesses Having Equivalent Circle Diameter of 0.20 μm to0.50 μm Existing on Surface of Magnetic Layer

(Area 40 μm×40 μm)

The following conditions were used as measurement conditions of the AFM,and the number of recesses having the equivalent circle diameter in therange described above (per 40 μm×40 μm area) was obtained regarding thesurface of the magnetic layer of the magnetic tape by the methoddescribed above.

The measurement regarding a region of the surface of the magnetic layerof the magnetic tape having an area of 40 μm×40 μm is performed with anAFM (Nanoscope 5 manufactured by BRUKER Corporation) in a peak forcetapping mode. SCANASYST-AIR manufactured by BRUKER Corporation is usedas a probe, a resolution is set as 512 pixels×512 pixels, and a scanspeed is set by the measurement regarding 1 screen (512 pixels×512pixels) for 512 seconds.

(7) Curvature of Magnetic Tape in Longitudinal Direction

The magnetic tape was taken out from the magnetic tape cartridge, andthe curvature of the magnetic tape in the longitudinal direction wasdetermined by the method described above.

(8) Total Thickness of Magnetic Tape (Tape Thickness)

Ten tape samples (for example, 5 cm in length) are cut out from anyportion of the magnetic tape, and the tape samples are stacked tomeasure the thickness. The thickness was measured using a digitalthickness gauge of a Millimar 1240 compact amplifier manufactured byMARH and a Millimar 1301 induction probe. The value (thickness per tapesample) obtained by calculating 1/10 of the measured thickness wasdefined as the tape thickness. For the magnetic tape, the tape thicknesswas 5.2 μm. The tape thickness was obtained in the same manner forExamples and Comparative Examples which will be described later, and thetape thickness was 5.2 μm in each case.

(9) Measurement of Transfer Rate

The magnetic tape cartridge was inserted into the magnetic recording andreproducing device, and data was recorded on the magnetic tape and therecorded data was reproduced. As the magnetic recording and reproducingdevice, a magnetic recording and reproducing device having theconfiguration shown in FIG. 4 which has 32 or more channels ofreproducing elements and recording elements with a reproducing elementwidth of 0.8 μm, and includes a recording and reproducing unit includingservo signal reading elements on both sides thereof.

After acclimatizing the magnetic tape cartridge and the magneticrecording and reproducing device to the measurement environment(atmosphere temperature of 20° C. to 25° C., relative humidity of 40% to60%) for 1 day or longer, the recording and reproducing were performedover the entire tape length and width. During the recording andreproducing described above, the maximum capacity of the magnetic tapewas recorded and reproduced using drive control software. In addition,during the recording and reproducing described above, a tension appliedin the longitudinal direction of the magnetic tape was changed due totension adjustment performed by the control device of the magneticrecording and reproducing device. For the recording and reproducingdescribed above, the transfer rate was calculated as the capacity(MB/sec) recorded or reproduced per unit time by dividing the “recordedor reproduced capacity” by the “time required for recording orreproducing”. In a case where the value calculated by dividing therecorded capacity by the time required for recording is different fromthe value obtained by dividing the reproduced capacity by the timerequired for reproducing, a lower value was adopted as the transferrate. Table 1 shows the transfer rate as a relative value with themaximum transfer rate of a combination of the magnetic recording andreproducing device and the magnetic tape of 100.0%.

The maximum transfer rate is obtained, for example, by the followingmethod.

Using LTO-G8 (Generation8) media, LTO-8 drive, and free software (IBMTape Diagnostic Tool-Graphical Edition) manufactured by IBM, the “ReadAnd Write Tests” command is used to record and reproduce the maximumcapacity, and “DataRate” can be obtained by reading the obtained logdata file. In a case of LTO-G8 media (uncompressed, full-height drive),a transfer rate of 100.0%=360 MB/sec can be obtained.

Examples 2 to 27 and Comparative Examples 1 to 19

A magnetic tape cartridge was manufactured and various evaluations wereperformed in the same manner as in Example 1, except that the items inTable 1 were changed as shown in Table 1.

The result described above is shown in Table 1 (Tables 1-1 and 1-2).

TABLE 1-1 Magnetic layer Number of recesses having equivalent circlediameter of 0.20 μm to Heat treatment Back coating layer forming 0.50 μmHeat Ferromagnetic Non-magnetic composition (per area 40 μm × 40treatment powder powder Polyethyleneimine Stearic acid μm) temperatureExample 1 BaFe PET 0.2 parts 0.4 parts 500 50° C. Example 2 BaFe PET 0.3parts 0.5 parts 400 60° C Example 3 BaFe PET 0.3 parts 0.7 parts 300 50°C. Example 4 BaFe PET 0.5 parts 1.0 part  200 50° C. Example 5 BaFe PET1.0 part  2.0 parts 100 60° C Example 6 BaFe PET 2.7 parts 5.3 parts 1050° C. Example 7 BaFe PET 0.2 parts 0.4 parts 500 60° C. Example 8 BaFePET 0.3 parts 0.5 parts 400 60° C. Example 9 BaFe PET 0.3 parts 0.7parts 300 60° C. Example 10 BaFe PET 0.5 parts 1.0 part  200 60° C.Example 11 BaFe PET 1.0 part  2.0 parts 100 60° C. Example 12 BaFe PET2.7 parts 5.3 parts 10 60° C. Example 13 BaFe PET 0.2 parts 0.4 parts500 70° C. Example 14 BaFe PET 0.3 parts 0.5 parts 400 70° C. Example 15BaFe PET 0.3 parts 0.7 parts 300 70° C. Example 16 BaFe PET 0.5 parts1.0 part  200 70° C. Example 17 BaFe PET 1.0 part  2.0 parts 100 70° C.Example 18 BaFe PET 2.7 parts 5.3 parts 10 70° C. Example 19 BaFe PEN0.2 parts 0.4 parts 500 70° C. Example 20 BaFe PEN 0.3 parts 0.5 parts400 70° C. Example 21 BaFe PEN 0.3 parts 0.7 parts 300 70° C. Example 22BaFe PEN 0.5 parts 1.0 part  200 70° C. Example 23 BaFe PEN 1.0 part 2.0 parts 100 70° C. Example 24 BaFe PEN 2.7 parts 5.3 parts 10 70° C.Example 25 SrFe1 PET 2.7 parts 5.3 parts 10 70° C. Example 26 SrFe2 PET2.7 parts 5.3 parts 10 70° C. Example 27 ε-iron oxide PET 2.7 parts 5.3parts 10 70° C. Reference circle center position Heat treatmentdeviation Modulus of (Deviation of center bending position of averageHeat elasticity of core winding around Curvature in minimum regionTransfer treatment for heat core for heat longitudinal reference circle)rate time treatment treatment direction [μm] [%] Example 1  5 hours 0.8GPa 0.6N 4 mm/m 99 99.1 Example 2  3 hours 0.8 GPa 0.6N 4 mm/m 96 99.0Example 3  5 hours 0.5 GPa 0.8N 4 mm/m 98 99.0 Example 4  5 hours 0.8GPa 0.6N 4 mm/m 98 99.1 Example 5  3 hours 0.8 GPa 0.6N 4 mm/m 95 99.1Example 6  5 hours 0.5 GPa 0.8N 4 mm/m 92 99.2 Example 7 10 hours 0.8GPa 0.8N 2 mm/m 80 99.5 Example 8 10 hours 0.8 GPa 0.8N 2 mm/m 77 99.6Example 9 10 hours 0.8 GPa 0.8N 2 mm/m 75 99.5 Example 10 10 hours 0.8GPa 0.8N 2 mm/m 76 99.4 Example 11 10 hours 0.8 GPa 0.8N 2 mm/m 76 99.5Example 12 10 hours 0.8 GPa 0.8N 2 mm/m 74 99.5 Example 13 10 hours 0.8GPa 0.8N 0 mm/m 55 100.0 Example 14 10 hours 0.8 GPa 0.8N 0 mm/m 52100.0 Example 15 10 hours 0.8 GPa 0.8N 0 mm/m 50 100.0 Example 16 10hours 0.8 GPa 0.8N 0 mm/m 51 100.0 Example 17 10 hours 0.8 GPa 0.8N 0mm/m 50 100.0 Example 18 10 hours 0.8 GPa 0.8N 0 mm/m 48 100.0 Example19 10 hours 0.8 GPa 1.2N 0 mm/m 54 100.0 Example 20 10 hours 0.8 GPa1.2N 0 mm/m 51 100.0 Example 21 10 hours 0.8 GPa 1.2N 0 mm/m 53 100.0Example 22 10 hours 0.8 GPa 1.2N 0 mm/m 50 100.0 Example 23 10 hours 0.8GPa 1.2N 0 mm/m 49 100.0 Example 24 10 hours 0.8 GPa 1.2N 0 mm/m 50100.0 Example 25 10 hours 0.8 GPa 0.8N 0 mm/m 50 100.0 Example 26 10hours 0.8 GPa 0.8N 0 mm/m 52 100.0 Example 27 10 hours 0.8 GPa 0.8N 0mm/m 48 100.0

TABLE 1-2 Number of recesses having equivalent circle diameter of 0.20μm to Heat treatment Back coating layer forming 0.50 μm HeatFerromagnetic Non-magnetic composition (per area 40 μm × 40 treatmentpowder powder Polyethyleneimine Stearic acid μm) temperature ComparativeExample 1 BaFe PET 0.0 parts 0.0 parts 2000 50° C. Comparative Example 2BaFe PET 0.0 parts 0.1 parts 1500 50° C. Comparative Example 3 BaFe PET0.1 parts 0.1 parts 1000 50° C. Comparative Example 4 BaFe PET 0.2 parts0.4 parts 700 50° C. Comparative Example 5 BaFe PET 4.0 parts 8.0 parts5 50° C. Comparative Example 6 BaFe PET 5.3 parts 10.7 parts  3 50° C.Comparative Example 7 BaFe PEN 0.0 parts 0.0 parts 2000 50° C.Comparative Example 8 BaFe PEN 0.0 parts 0.1 parts 1500 50° C.Comparative Example 9 BaFe PEN 0.1 parts 0.1 parts 1000 50° C.Comparative Example 10 BaFe PEN 0.2 parts 0.4 parts 700 50° C.Comparative Example 11 BaFe PEN 4.0 parts 8.0 parts 5 50° C. ComparativeExample 12 BaFe PEN 5.3 parts 10.7 parts  3 50° C. Comparative Example13 BaFe PET 2.7 parts 5.3 parts 10 50° C. Comparative Example 14 BaFePET 0.0 parts 0.0 parts 2000 70° C. Comparative Example 15 BaFe PET 0.0parts 0.1 parts 1500 70° C. Comparative Example 16 BaFe PET 0.1 parts0.1 parts 1000 70° C. Comparative Example 17 BaFe PET 0.2 parts 0.4parts 700 70° C. Comparative Example 18 BaFe PET 4.0 parts 8.0 parts 570° C. Comparative Example 19 BaFe PET 5.3 parts 10.7 parts  3 70° C.Reference circle center position Heat treatment deviation Modulus of(Deviation of center bending position of average Heat elasticity of corewinding around Curvature in minimum region Transfer treatment for heatcore for heat longitudinal reference circle) rate time treatmenttreatment direction [μm] [%] Comparative Example 1 5 hours 0.5 GPa 0.6N5 mm/m 142 94.0 Comparative Example 2 5 hours 0.5 GPa 0.6N 5 mm/m 14594.1 Comparative Example 3 5 hours 0.5 GPa 0.6N 5 mm/m 140 94.1Comparative Example 4 5 hours 0.5 GPa 0.6N 5 mm/m 143 94.0 ComparativeExample 5 5 hours 0.5 GPa 0.6N 5 mm/m 139 93.9 Comparative Example 6 5hours 0.5 GPa 0.6N 5 mm/m 141 94.0 Comparative Example 7 5 hours 0.5 GPa0.6N 5 mm/m 143 94.1 Comparative Example 8 5 hours 0.5 GPa 0.6N 5 mm/m144 94.0 Comparative Example 9 5 hours 0.5 GPa 0.6N 5 mm/m 139 94.0Comparative Example 10 5 hours 0.5 GPa 0.6N 5 mm/m 142 94.0 ComparativeExample 11 5 hours 0.5 GPa 0.6N 5 mm/m 140 94.1 Comparative Example 12 5hours 0.5 GPa 0.6N 5 mm/m 137 94.0 Comparative Example 13 10 hours  0.5GPa 0.6N 5 mm/m 115 95.0 Comparative Example 14 10 hours  0.8 GPa 0.8N 0mm/m 119 95.0 Comparative Example 15 10 hours  0.8 GPa 0.8N 0 mm/m 11695.0 Comparative Example 16 10 hours  0.8 GPa 0.8N 0 mm/m 115 95.1Comparative Example 17 10 hours  0.8 GPa 0.8N 0 mm/m 116 95.1Comparative Example 18 10 hours  0.8 GPa 0.8N 0 mm/m 117 95.0Comparative Example 19 10 hours  0.8 GPa 0.8N 0 mm/m 115 95.0

As shown in Table 1, in the examples, recording and reproduction at ahigher transfer rate than in the comparative example was possible.

A magnetic tape cartridge was manufactured by the method described aboveas in Example 1 except that the homeotropic alignment process was notperformed in a case of manufacturing the magnetic tape.

A sample piece was cut out from the magnetic tape taken out from themagnetic tape cartridge. For this sample piece, a vertical squarenessratio SQ was obtained by the method described above using aTM-TRVSM5050-SMSL type manufactured by Tamagawa Seisakusho Co., Ltd. asan oscillation sample type magnetic-flux meter and it was 0.55.

The magnetic tape was also taken out from the magnetic tape cartridge ofExample 1, and the vertical squareness ratio was obtained in the samemanner for the sample piece cut out from the magnetic tape, and it was0.60.

The magnetic tapes taken out from the above two magnetic tape cartridgeswere attached to each of the ½-inch reel testers, and theelectromagnetic conversion characteristics (signal-to-noise ratio (SNR))were evaluated by the following methods. As a result, regarding themagnetic tape taken out from the magnetic tape cartridge of Example 1, avalue of SNR 2 dB higher than that of the magnetic tape manufacturedwithout the homeotropic alignment process was obtained.

In an environment of a temperature of 23° C. and a relative humidity of50%, a tension of 0.7 N was applied in the longitudinal direction of themagnetic tape, and recording and reproduction were performed for 10passes. A relative speed of the magnetic head and the magnetic tape wasset as 6 m/sec. The recording was performed by using a metal-in-gap(MIG) head (gap length of 0.15 μm, track width of 1.0 μm) as therecording head and by setting a recording current as an optimalrecording current of each magnetic tape. The reproduction was performedusing a giant-magnetoresistive (GMR) head (element thickness of 15 nm,shield interval of 0.1 μm, reproducing element width of 0.8 μm) as thereproduction head. A signal having a linear recording density of 300kfci was recorded, and the reproduced signal was measured with aspectrum analyzer manufactured by ShibaSoku Co., Ltd. In addition, theunit kfci is a unit of linear recording density (cannot be converted toSI unit system). As the signal, a sufficiently stabilized portion of thesignal after starting the running of the magnetic tape was used.

One embodiment of the invention is advantageous in a technical field ofvarious data storages such as backup or archives.

What is claimed is:
 1. A magnetic tape container comprising: a corearound which a magnetic tape is wound, wherein the magnetic tapeincludes a non-magnetic support, and a magnetic layer including aferromagnetic powder, and a maximum value of a deviation of a centerposition of an average minimum region reference circle of a trajectoryof one rotation drawn by the magnetic tape, in a case where the woundmagnetic tape is drawn out from the core core is 100 μm or less forthree points of the magnetic tape in a width direction.
 2. The magnetictape container according to claim 1, wherein the magnetic tape has aservo pattern in the magnetic layer.
 3. The magnetic tape containeraccording to claim 1, wherein an entire length of the magnetic tape is200 m or more.
 4. The magnetic tape container according to claim 1,wherein the maximum value of the deviation of the center position of theaverage minimum region reference circle is 80 μm or less for the threepoints.
 5. The magnetic tape container according to claim 1, wherein themaximum value of the deviation of the center position of the averageminimum region reference circle is 55 μm or less for the three points.6. The magnetic tape container according to claim 1, wherein themagnetic tape further includes a non-magnetic layer including anon-magnetic powder between the non-magnetic support and the magneticlayer.
 7. The magnetic tape container according to claim 1, wherein themagnetic tape further includes a back coating layer including anon-magnetic powder on a surface side of the non-magnetic supportopposite to a surface side on which the magnetic layer is provided. 8.The magnetic tape container according to claim 1, wherein the magnetictape container is a magnetic tape cartridge.
 9. The magnetic tapecontainer according to claim 8, wherein the magnetic tape has a servopattern in the magnetic layer.
 10. The magnetic tape container accordingto claim 8, wherein an entire length of the magnetic tape is 200 m ormore.
 11. The magnetic tape container according to claim 8, wherein themaximum value of the deviation of the center position of the averageminimum region reference circle is 80 μm or less for the three points.12. The magnetic tape container according to claim 8, wherein themaximum value of the deviation of the center position of the averageminimum region reference circle is 55 μm or less for the three points.13. The magnetic tape container according to claim 1, wherein themagnetic tape container is a magnetic recording and reproducing device,and further includes a magnetic head.
 14. The magnetic tape containeraccording to claim 13, wherein the magnetic tape has a servo pattern inthe magnetic layer.
 15. The magnetic tape container according to claim13, wherein an entire length of the magnetic tape is 200 m or more. 16.The magnetic tape container according to claim 13, wherein the maximumvalue of the deviation of the center position of the average minimumregion reference circle is 80 μm or less for the three points.
 17. Themagnetic tape container according to claim 13, wherein the maximum valueof the deviation of the center position of the average minimum regionreference circle is 55 μm or less for the three points.
 18. The magnetictape container according to claim 13, wherein the magnetic head includesa reproducing element having a reproducing element width of 0.8 μm orless.
 19. The magnetic tape container according to claim 13, furthercomprising: a tension adjusting mechanism which adjusts a tensionapplied in a longitudinal direction of the magnetic tape which runs inthe magnetic recording and reproducing device.
 20. The magnetic tapecontainer according to claim 1, wherein the magnetic tape has a verticalsquareness ratio of 0.60 or more.